AU2005313616B2

AU2005313616B2 - Device and method for detecting material by way of gravitational field analysis

Info

Publication number: AU2005313616B2
Application number: AU2005313616A
Authority: AU
Inventors: Felix Raffalt
Original assignee: Vega Grieshaber KG
Current assignee: Vega Grieshaber KG
Priority date: 2004-12-07
Filing date: 2005-11-10
Publication date: 2011-03-17
Anticipated expiration: 2025-11-10
Also published as: EP1820048A1; WO2006061077A1; EP1820048B1; AU2005313616A1

Description

DEVICE AND METHOD FOR DETECTING MATERIAL BY WAY OF GRAVITATIONAL FIELD ANALYSIS The present invention relates to the detection of material by way of gravitational field analysis. In particular, the present invention relates to a gravimeter unit for determining a gravitational field intensity, to a sensor for detecting material by way of gravitational field analysis, to a method for fill level measuring of a product in a tank, to the use of a sensor as a fill-level measuring device, to the use of a sensor as a proximity switch, to a program element for fill level measuring, and to a computer-readable storage medium. Every body which comprises mass generates a gravitational field that exerts an attraction force to other masses. In the case of a spherical body with homogeneous mass distribution the gravitational field at the surface of the body is proportional to the diameter of the sphere and the density of the body. Outside the body the field intensity of its gravitational field decreases towards the centre of the sphere at a reciprocal value of the distance square. At the earth's surface, the value of the gravitational field of the earth, which gravitational field acts to accelerate gravity, is approximately 9.81 metres per square second. A spherical volume of water 1 m in diameter generates an intrinsic gravitational field that is in the ratio of 1 : 70,000,000 when compared to the earth's field. While this value is extremely small it may, however, be measured by means of a gravimeter unit. As a rule, these devices comprise a precision-mechanical mass-spring system onto which the gravitational field to be measured acts. In this arrangement the spring is elongated by the gravitation-proportional weight of the mass element, and its change in length, or a compensation force required to -2 attain a defined reference length, is used as a measure for the experienced gravitational field intensity. Furthermore, gravity pendulums, floating bodies and falling-ball arrangements are used for measuring gravitational fields. Apart from scientific applications, such as measuring the tidal forces generated by the moon and the sun, gravimeter instruments are primarily used in finding and exploring for mineral resources, such as deposits of crude oil, gas, coal, ores and salts. The fact that as a rule these materials have a density that differs from that of normal subsurface rock, or that these materials change in density when they are contained in the pores of rock, is utilised. In a region to be explored, a gravimeter instrument is moved along the earth's surface, and the measured gravitational values as well as their geographical positions are documented. A gravimeter can also be installed on an aircraft that flies over the region to be explored. Furthermore, it is common practice to lower gravimeter instruments into boreholes and during the lowering-down procedure to document the measured gravitational field values and the associated depth values. On the basis of such measuring sequences, maps are produced that show geological anomalies in the gravitational field, or depth diagrams are produced that show the subsurface region of the field. By means of the maps and diagrams prepared, a trained geologist may detect existing differences in density in the subsurface region of the earth, and in this way may draw conclusions about any mineral deposits and their potential for exploitation.

-3 US 6,612,171 Bi discloses a gravimeter for measuring the gravitational field in boreholes in order to determine the density of formations in the subsurface region of the earth. In this arrangement the disclosed gravimeter can be moved between two positions in order to carry out differential measuring. DE 689 15 T2 discloses a gravitation gradiometer. It is intended for measuring extra-diagonal components of a gravitation gradient sensor; in particular a special bending pivot bearing is disclosed. WO 98/57197 also discloses a gravity gradiometer. The document explains that gravity measuring is often carried out from aircraft in order to detect crude oil deposits. With the gravity gradiometer described in this printed publication, it is apparently possible to compensate for instances of acceleration that occur in the aircraft and that thus have an influence on the gravity gradiometer. All the known gravimeter devices are unsuitable for use as industry-standard sensors for the detection of material quantity or for determining the level of a product in a tank. These gravimeter devices are far too expensive, too bulky and only able to display the gravitational field in one spatial direction. The gravitational field display produced requires interpretation by a specialist in order to derive further information from it. Furthermore, the response times of known gravimeter systems are far too slow and their power consumption is far too high for an industrial fill level sensor. There exists a need to provide a sensor for direct measuring and output of a fiill level value.

-4 According to an exemplary embodiment of the, present invention, there is disclosed a gravimeter unit for determining a gravitational field intensity, with the gravimeter unit comprising a first floating body, a first detector and a source for generating a field, wherein the first floating body can be kept afloat in a contactless manner by a field generated by the source, wherein a first position of the first floating body can be detected by the first detector, wherein the gravimeter unit is designed to determine first data based on the detected first position or the generated field, and wherein the first data correspond to a first gravitational field intensity in a first location. Advantageously, an economical miniaturised hiqh-resolution gravimeter measuring cell can thus be provided, in which a gravity-field detecting mass element is kept afloat in a contactless three-dimensional manner by means of electrostatic force fields. There is thus no necessity to provide a mechanical spring element. The present invention according to this aspect is based on the idea of measuring, by way of a floating mount of a floating body, the gravitational force that acts on said floating body. For example, a knowledge of the compensation force that is needed to hold the floating body in its original position or to return it to its original position can be used to draw conclusions relating to the gravitational force acting on the floating body. The invention thus provides a cost-effective miniaturised high resolution gravimeter unit by means of which unit gravitational field intensities can be determined three dimensionally without any mechanical spring elements or the like. The fIJcating ass elemet .s preferably arranged directLy abo-:;e anui nt grated semiconducLor ci rcuit so that , for -5 example, the detector and the source can at least in part be affixed directly to said semiconductor circuit. According to a further exemplary embodiment of the present invention, the field is selected from the group comprising an electrical field, a magnetic field, an electromagnetic field and a mechanical flow field. Advantageously it is thus possible, by way of corresponding components such as, for example, coils or capacitor plates, in an easy manner to generate fields that keep the floating body afloat. According to a further exemplary embodiment of the present invention, the first detector is designed for capacitive, inductive, conductive or optical detection of the first position of the first floating body. Capacitive position detection can, for example, take place by way of a second electrode that can be used for capacitance measuring between the floating body and the second electrode. According to an aspect of the present invention the floating body can, for example, be arranged within a hollow space that has been filled with a dielectric. This arrangement can enhance the sensitivity of capacitive measuring or it can also e.g. stabilise the floating body. Of course, capacitive position detection can also take place by way of a pair of electrodes. For the purpose of inductive measuring, for example miniaturised coils can be integrated in the gravimeter unit, which coils generate a magnetic field that has an effect on the floating body. For example, induction currents can be generated in the floating body. optical position determination provides an advantage, apart from radiation pressure of the photons, in that it does not couple any additional forces into the floating body. For -6 example, in this context interferometric methods as known from the field of optics can be used. According to a further exemplary embodiment of the present invention the gravimeter unit further comprises a second floating body and a second detector, wherein a second position of the second floating body can be detected by the second detector, and wherein the gravimeter unit is adapted to generate the first data on the basis of the measured first position and of the measured second position. Advantageously, by using two floating bodies within the gravimeter unit, calibrations can be carried out, i.e. ageing processes or drift in the measured data as a result of fluctuations in temperature can be compensated for. It should be noted that the gravimeter unit, although it determines the first position of the first floating body and the second position of the second floating body, from this only generates one data record that provides information about the gravitational field at the location of the gravimeter unit. The use of several floating bodies in the gravimeter unit can thus enhance system accuracy and system reliability, but in the present case only furnishes a shared data record. According to a further exemplary embodiment of the present invention, the gravimeter unit further comprises a control device, which is adapted to hold the first floating body in its home position. For example, the control device can send control signals to the source so as to generate the field so that the field intensity is varied accordingly in order to counteract changed gravitational acceleration, and in order to compensate for the excursion of the floating body from the zero position. According to the invention, the control -7 variables that are used to compensate for instances of changed gravitational acceleration can be taken into consideration when the gravitational field intensity is determined. According to a further exemplary embodiment of the present invention, the gravimeter unit further comprises a storage device for storing reference values. Furthermore, it is possible to store these reference values in the storage device as part of a procedure of calibrating the gravimeter unit, and thus to simplify or calibrate subsequent readings. By installing a storage device in the gravimeter unit, data exchange between the gravimeter unit and external analysis units or display units can be minimised. According to a further exemplary embodiment of the present invention, a sensor for material detection by means of gravitational field analysis is stated, with the sensor comprising a first gravimeter unit, a second gravimeter unit and a communication interface. The first gravimeter unit is adapted to determine first data that corresponds to a first gravitational field intensity at a first location. The second gravimeter unit is adapted to determine second data that corresponds to a second gravitational field intensity at a second location, and the communication interface is adapted to transmit the first data and the second data to an analysis unit. Differentiation between a gravitational field which, for example, originates from a product to be detected, and the remaining gravitational fields that originate from masses that are not to be measured, particularly advantageously takes place in that the gradient values of the gravitational field in the region of the product to be measured are determined, and in that from their spatial -8 gradient the mass distribution in the near surroundings is determined. Advantageously, according to this exemplary embodiment of the present invention, the gravitational field intensity near the mass to be detected is measured at various points in space. Since the distances between the gravity measuring points and the mass to be detected are known, by means of the encountered field gradient values it is possible to determine the share of the measured cumulative field intensity, which share is attributable, at the observer position, to the unknown mass. According to this exemplary embodiment of the present invention, an industry sensor is stated, in particular a sensor for determining tank fill levels, which industry sensor makes it possible to measure materials, in particular the product in the tank, in a contactless manner through the closed walls of the tank. The tank level is determined by the sensor by measuring and analysing the product's intrinsic gravitational field. Advantageously, all the requirements are met, which requirements are demanded from a sensor for use in industrial plant. To this effect the sensor is of a static design, without a gravimeter instrument being mechanically moved over a measuring path or a surface. The generated measuring result does not require any further processing or interpretation by an expert; instead it can present the directly displayable fill value. Said fill value can be available continuously, without any interruptions and in real time. The measuring result does not contain any geological or astronomical components such as fluctuating water content of the subsurface of the earth, tectonic mass displacement in the earth's mantle, or tidal forces as they are in particular measured by conventional gravitation sensors. Similarly, any masses, such as people and vehicles, which - 9 masses move in the surroundings, can be suppressed in the measuring result. According to a further exemplary embodiment of the present invention, the determined first data is based on first floating-body position data or on first control parameters of a first control device. Furthermore, the determined second data is based on second floating-body position data or on second control parameters of a second control device. The floating-body position or the control parameters, which can for example be a voltage applied to a capacitor plate, represent data which must be easily measurable and precisely determinable, by way of which data well-founded conclusions about corresponding gravitational forces that act on the floating body can be made. According to one aspect of the present invention the first and the second gravimeter units are arranged in the sensor at fixed positions relative to each other. Furthermore, the two gravimeter units can be spaced apart in the factory in such a way that optimum measuring is possible, for example, in relation to a very specific tank. According to a further exemplary embodiment of the present invention, the first gravimeter unit is arranged so as to be rotatable on an axis or slidable along an axis, wherein during rotation or displacement, data is continuously acquired, which data is based on the detected first positions or the generated fields within the gravimeter unit. This acquired data can then be combined to form a volume data record which represents the topology of a gravitational field. By way of this volume data record it is thus possible to draw conclusions concerning local mass distribution in the surroundings of the sensor. In order to analyse the data record and to display an image, known methods, e.g. from computer tomography, can be used.

- 10 According to one aspect of the present invention the sensor comprises a plurality of gravimeter units that are arranged along a line, on an area or spatially so that a one- two or three-dimensional data record can be determined, which represents a gravitational field distribution. Furthermore, the sensor may comprise an analysis unit which is adapted to receive the first data and the second data from the communication interface, wherein the analysis unit is designed to calculate the gradient of a gravitational field on the basis of the first data and the second data. According to one aspect of the present invention, the analysis unit together with the sensor can, for example, be provided on a semiconductor chip in the form of an integrated circuit. Of course, it is also possible for the analysis unit to be arranged externally and to receive data from the communication interface for example by way of radio transmission or some other wireless data transmission method. Of course, the communication interface can also be connected to the analysis unit by way of a data line. According to a further exemplary embodiment of the present invention, the use of a sensor according to the invention as a fill-level measuring device is stated. To this effect the sensor can be arranged near a tank and can measure the level inside the tank. Furthermore, according to one aspect of the invention, the sensor can be used as a proximity sensor which detects, for example, whether a door is open or closed, or which detects the distance of a corresponding object from the sensor, or the speed with which the object approaches the sensor. According to a further exemplary embodiment of the present invention, the use of a gravimeter as a fill-level - 11 measuring device is stated, which gravimeter, for example, carries out a method for fill level measuring according to an embodiment of the present invention. Moreover, according to one aspect of the present invention, a gravimeter can be used as a proximity sensor, for example in order to detect distances. According to a further exemplary embodiment of the present invention, the use of a gravimeter unit as an acceleration meter is stated, which gravimeter unit is used for measuring instances of acceleration, for example within a vehicle, aircraft or some other moving or oscillating object, for example a person or a machine. According to a further exemplary embodiment of the present invention, a method for measuring the fill level of a product in a tank by means of gravitational field analysis is stated, wherein the method comprises the following steps: determining first data which corresponds to a first gravitational field intensity in a first location, by a first gravimeter unit; determining second data which corresponds to a second gravitational field intensity in a second location, by a second gravimeter unit; calculation of a fill level of the product, on the basis of the determined first and second data. Advantageously, the use of gravitational field analysis for fill level measuring allows contactless measuring, i.e. no contact is required with the object to be measured. Furthermore, the method according to the invention does not require any radiation source or the like which emits a measuring beam that is, for example, subsequently reflected by the product so that it is subsequently possible to make statements about the fill height. Instead, the method according to the invention measures gravitational fields that are generated by the product. This does not require -12 the sensor to be placed in the tank. Nor is there any energy introduced into the product as a result of measuring. According to an exemplary embodiment of the present invention, there is provided a gravimeter unit for determining a gravitational field intensity. The gravimeter 5 unit comprises: a source for generating a field, the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; a first floating body that can be kept afloat in a contactless manner by a field generated by the source; a first detector, a first position of the first floating body can be detected by the first detector, the first detector comprising a second electrode for detecting the first 1o position of the first floating body; wherein the gravimeter unit is adapted to determine first data on the basis of the detected first position or of the generated field, the first data corresponding to a first gravitational field intensity in a first location, the gravimeter unit being provided on a semiconductor chip. According to a further exemplary embodiment of the present invention, there is is provided a sensor for material detection by means of gravitational field analysis. The sensor comprises: a first gravimeter unit according to the above embodiment adapted to determine first data that corresponds to a first gravitational field intensity at a first location; a second gravimeter unit according to according to the above embodiment adapted to determine second data that corresponds to a second gravitational field intensity 20 at a second location; and a communication interface adapted to transmit the first data and the second data to an analysis unit. According to a further exemplary embodiment of the present invention, there is provided a method for fill level measuring a product in a tank by means of gravitational field analysis. The method comprises the following steps: generating a field by a source, 25 the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field generated by the source, the first detector comprising a second electrode for detecting the first position of the first floating body; determining first data 30 corresponding to a first gravitational field intensity at a first location, by the first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; determining second data corresponding to a second gravitational 812369 (3212956_1) -13 field intensity at a second location, by a second gravimeter unit; calculating a fill level of the product, on the basis of the determined first and second data. An aspect of the present invention also relates to a program element for measuring the fill level of a product in a tank by means of gravitational field analysis, 5 wherein the program element when it is executed on a processor instructs the processor to carry out the following operations: generating a field by a source, the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field io generated by the source, the first detector comprising a second electrode for detecting the first position of the first floating body; determining first data corresponding to a first gravitational field intensity at a first location, by a first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; determining second data corresponding to a second gravitational field intensity at a is second location, by a second gravimeter unit; calculating a fill level of the product on the basis of the determined first and second data. The program element according to an exemplary embodiment of the present invention may preferably be loaded into the working memory of a data processor. The data processor may be adapted so that it may implement exemplary embodiments of the 20 method according to the present invention. Moreover, the computer program may be written in any programming language, for example in C++ and may be stored on a computer-readable storage medium, such as for example a CD-ROM. Furthermore, the computer program may be available over a network such as for example the WorldWideWeb, from which it may be loaded into a processor or computer. 25 According to another aspect of the present invention, there is disclosed a computer-readable storage medium on which a computer program for measuring the fill level of a product in a tank by means of gravitational field analysis is stored, wherein the computer program when it is executed on a processor instructs the processor to carry out the following operations: generating a field by a source, the field being an electrical field, 30 the source comprising at least a first electrode for generating the electrical field; detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field generated by the source, the first detector comprising a second electrode for detecting the first position of the first 812369(3212956_1) -13A floating body; determining first data corresponding to a first gravitational field intensity at a first location, by a first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; determining second data corresponding to a second gravitational field intensity at a second location, by a second 5 gravimeter unit; calculating a fill level of the product on the basis of the determined first and second data. Below, the invention is described in more detail by means of exemplary embodiments with reference to the drawings. Fig. I shows a cross section of an exemplary embodiment of a gravimeter unit 10 according to the present invention. Fig. 2 shows a top view of a semiconductor chip with electrodes placed thereon, of the embodiment shown in Fig. 1, of the gravimeter unit according to the invention. Fig. 3 shows a cross section of a further exemplary embodiment of a gravimeter unit according to the present invention. Is Fig. 4 shows a top view of a semiconductor chip with electrodes placed thereon, of the exemplary embodiment of the gravimeter unit shown in Fig. 3. Fig. 5 shows a cross section of an exemplary embodiment of a gravimeter unit according to a further exemplary embodiment of the present invention. Fig. 6 shows a diagrammatic lateral view of a gravitational fill-level limit switch, 20 which is horizontally installed on the side of a product tank, according to an exemplary embodiment of the present invention. Fig. 7 shows a diagrammatic cross-sectional view of a partly filled product tank, on which five different types 812369 (3212956_1) - 14 of continuously measuring sensors according to exemplary embodiments of the present invention are installed. Fig. 8 shows a further exemplary embodiment of a gravimeter according to the present invention. Fig. 9 shows a further exemplary embodiment of a gravimeter according to a further exemplary embodiment of the present invention. Fig. 1 shows a cross section of an exemplary embodiment of a gravimeter unit according to the present invention, which embodiment will be explained in more detail further below. Several of these gravimeter units can be integrated in a fill level sensor or in a fill-level limit switch. A corresponding exemplary embodiment is shown in Fig. 6. Fig. 6 shows a diagrammatic lateral view of a gravitational fill-level limit switch, which is horizontally installed on the side of a product tank, according to an exemplary embodiment of the present invention The fill level sensor according to the invention comprises at least 2 gravimeter units G1, G2, which are installed at fixed positions on, or in direct proximity to, the product tank to be measured. In order to compensate for varying gravitational far fields, whose origin is not due to changes in the fill level, for further processing of the signals the field-intensity measuring values of the two or more gravimeter units are subtracted from each other. In this arrangement the field-differential value formation is to be carried out so as to be directionally selective, in other words field components which have the same orientation in relation to the x-, y- or z-spatial axis are to be subtracted from each other.

- 15 Depending on the number of gravimeter units and their positions on the product tank, the fill level value is determined, from the field differential values, according to various methods that will be presented later. A novel miniature gravimeter is used for gravitational field measuring. An exemplary embodiment of it is shown in Fig. 1. Differentiation between the gravitational field which originates from the product to be detected, and the remaining gravitational fields that originate from masses that are not to be measured, particularly advantageously takes place in that the gradient values of the gravitational field in the region of the product to be measured are determined, and in that from their spatial gradient the mass distribution in the near surroundings is determined. Since the gravitational field of each body, outside this body, decreases towards its centre of gravity at a reciprocal value of the distance square, in the near surroundings of said body there is a significantly greater percentage reduction in the field intensity per unit of length than is the case further away. The gravitational fields of bodies that are located at various distances thus have an individual spatial gradient change value and can therefore be distinguished by means of said gradient-change value. A small mass situated nearby which has a very weak intrinsic gravitational field can thus, due to its large field-gradient change value, be measured despite the dominating strong earth field, whose gradient change value is, however, smaller by many powers of ten.

- 16 For this purpose the gravitational field intensity near the mass to be detected is measured at various points in space. Since the distances between the gravitational measuring points and the mass to be detected are known, by means of the encountered field gradient values it is possible to determine the share of the measured cumulative field intensity, which share is attributable, at the observer position, to the unknown mass. For many applications in practical use it is sufficient if the gravitational measuring points are on a straight line that points towards the mass to be detected. In such a gravitational field sensor the individual gravimeter measuring cells register a differently weakened object field intensity as a function of their distance from the target object. Due to the large field-gradient change value in the near region of the measuring object, weakening is clearly non-linear. In contrast to the above, objects located further away, depending on the spatial sensor alignment, either generate identical field intensities in the measuring cells, or, due to their low field-gradient change values in the far region, create an almost linear field reduction along the measuring cells. By corresponding mathematical processing of the cell measuring values, the sensor electronics can compute-out the far fields. In contrast to electromagnetic and acoustic waves, gravitational fields are not subject to the physical phenomena of absorption, reflection, dispersion, interference, diffraction and refraction. If the hand of a human being is trans-illuminated by a light source, then the exiting light does not make it possible to detect the bone structure. Even with the use of - 17 highly sophisticated optical sensors and the most complex of data processing algorithms it is not possible to generate a bone image in this way. The reason for this is due to the previously mentioned physical phenomena having destroyed the information content of the light. Since in the case where a gravitational field passes through a layer of material none of these effects has any influence, the information content of the passing field is not affected in any way. This means that the gravitational field of a glass of water placed behind a thick plate of lead passes completely unchanged through the plate, so that there is no difference whether or not the plate is in place. The plate of lead merely adds its own gravitational field to the gravitational fields already existing in the space. Since each of the fields has its own origin in space, an analysis of the spatial field-distribution renders a separation possible. The possibility of detecting, through the plate of lead, the fill level of the glass, or even the shape of the glass, thus merely depends on the accuracy and resolution of the available gravity sensor technology. Below, firstly, measuring according to the invention, of fill-level limit values, by analysing the product's inherent gravitational field, is described. Level-detection switching sensors are intended to signal when a specified fill level has been reached. To this effect the sensor is attached to the outside of the tank wall at the height of the level value to be signalled. It is the task of the sensor to monitor a spatially limited volume for the presence of a product mass. Masses that are situated outside the tank must not be indicated.

- 18 A fill-level limit switch comprises, for example, three gravimeter circuits by means of which the gravitational field intensity is measured at three different points. The points are preferably situated on a straight line which points towards the level value to be measured. From the three measuring values obtained, two adjacent field gradient values can be determined by means of subtraction. While the field intensity increases proportionally to the diameter of the product, the field gradient on the fill level surface is independent of the diameter of the product volume. Both the field intensity and the gradient are both proportional to the product density. With an increase in the distance from the product surface, the field intensity and the field gradient decrease. The degree of the distance-related decrease of both parameters is a function of the product diameter and thus of the tank size. When determining the installation spacing of the three gravimeters within the fill level sensors, the region of the tank diameters to be covered has to be taken into account. If the selected spacing is too wide, the sensor can see through smaller tanks so that masses that are located behind are detected. If the selected spacing is too narrow, large tanks return only small signal differences between the gravimeters. Since gravimeters do not influence each other, for the purpose of enlarging the field of application, in addition a fourth gravimeter with a larger spacing can be provided in the sensor. Fig. 6 diagrammatically shows a gravitation fill-level limit switch which is horizontally installed on the side of a product tank.

- 19 The gravimeter circuits that are located in the sensor housing are designated G1, G2, G3. The spacing a 2 , a 3 between the gravimeters is, for example, 20 mm in each case. The spacing a, between the first gravimeter G1 and the product tank is, for example, 10 mm, while the spacing a 4 from the rear wall of the sensor housing is, for example, 80 mm. The mass of the product tank m(B) is, for example, 1 kg, at a diameter of 0.124 m; while the masses of the interference elements Si and S 2 are, for example, 100 kg in each case, at a diameter of 0.58 m in each case. Of course, it is also possible to select entirely different spacing, densities and masses. Sensor signal processing detects the presence of a product firstly in that the field gradient between the two gravimeters nearest the product is of a certain magnitude, which indicates that adequate mass density is present, and secondly in that the field gradient further away from the product in a particular manner is lower than the first gradient, which indicates that the detected mass is in close proximity and in the correct direction. In order to eliminate fluctuating far fields, the sensor signal processing device first forms the differential values (G1 - G2) and (G2 - G3) of the field intensities situated in the direction of the measuring straight. These values are proportional to the field gradient in the corresponding path interval. Subsequently, with reference to the extent of the first differential value, the signal processing device determines two permissible value ranges in relation to the second differential value. If the second differential value is in the first value range, then the sensor outputs an "empty" message. If the value is in the second value range, a "full" message is output. If the second differential value is not contained in either of the two associated value - 20 ranges, then there is a malfunction, and the sensor outputs a malfunction message. If the sensor is to be equipped with a switching hysteresis, this can take place by using different value ranges in relation to the empty/full and full/empty change. In the case of sensors that are being used as maximum-level or minimum-level safety limit switches, it may make sense to allocate a value range of its own to each of these two operating modes so as to accord signal output preference to the sensor output value that is reliable in relation to the respective operating mode. By means of mathematical functions stored in the sensor, which functions have the first differential value as an input variable, the sensor electronics can compute the limits of the allocation ranges of the second differential value to the output states empty/full/malfunction. It is also possible, instead of mathematical functions, to store a value table in the sensor, from which value table the sensor-signal processing device, on the basis of the first differential value, can read the corresponding range allocation limits in relation to the second differential value. In order to limit the size of the value table, a sensible number of input values is used, and in the case of in-between values, interpolation according to known methods takes place. There is also the option of matching to the actual measuring task the required minimum value of the first differential value and the range allocation limits in relation to the second differential value in addition by* means of entered measuring application characteristics such as the diameter of the tank or the density of the product.

- 21 Likewise it is possible to carry out full calibration with a full tank in order to adapt the signal analysis parameters to the actually occurring field differential values. By means of the measuring arrangement shown in Figure 6, below, the influence which external masses and their distance has on the measuring result is shown. The product tank used in the example is very small; when it is full it holds a product quantity of only 1 kg in weight. It is the function of the laterally installed sensor to reliably indicate the presence of this quantity without being influenced by variable masses all around. In order to demonstrate the influence that movable mass bodies have, in Figure 6 the parasitic masses Si and S 2 are shown. By way of example, these are two persons that are heavily overweight, with a spherical belly weighing 100 kg each. Both persons assume the most critical position from the point of view of the measuring arrangement, in that the centre of gravity of the belly is precisely on the measuring straight of the three gravimeters G1, G2, G3. To this effect, the first person (parasitic mass Si) is standing precisely at the rear of the tank; the body of the second person (parasitic mass S 2 ) directly contacts the sensor housing from the rear. It has been assumed that the density of the product and of the parasitic masses is 1 g/ccm (water) . For ease of calculation, all masses have a spherical volume. The thickness of the tank wall is 10 mm.

- 22 Table 1 asitic Parasitic G G G Diff. value Diff. value Diff. s 1 mass 2 1 2 3 Gi-G2 G2-G3 value [kg] [nm/s 2 ] [nm/s 2 ] [nm/s 2 ] [nm/s 2 ] (Gi-G 2 )

(G

2

-G

3 ) - 37.1 33.8 31.0 3.3 2.8 0.5 100 -39.7 -43.9 -48.7 4.2 4.8 -0.6 100 -2.6 -10.1 -17.7 7.5 7.6 -0.1 - 12.9 7.9 5.3 5.0 2.6 2.4 - 50.0 41.7 36.3 8.3 5.4 2.9 100 -26.8 -36.0 -43.4 9.2 7.4 1.8 100 10,3 -2.2 -12.4 12,5 10,2 2.3 - 23 With reference to seven different mass combinations, Table 1 shows the occurring field intensity values at the three gravimeters, as well as the differential values calculated therefrom. The field intensities are stated in nanometres per square second and apply in the direction of the measuring straight. The first three lines of the table show the field values with the tank empty and with parasitic masses present. The fourth line shows the field values with the tank full, without the parasitic masses. The last three lines show the field values with the tank full and with parasitic masses present. The table shows that in the case of parasitic masses without a product, while the first field differential value unequivocally indicates the presence of a mass, the difference to the second differential value is however only minimal. This means that the detected mass is located outside the spatial volume to be observed, and must therefore not be displayed. In the case of the parasitic masses with product, the table shows that not only is the first differential value high, but the difference to the second differential value is sufficient for outputting the desired "full" message. Although each of the two parasitic masses in the example was 100-times as large as the product mass, the gravitational field sensor was able to correctly display the fill level. The values of Table 1 also show that if only two instead of three gravimeters were used, it would not be possible to differentiate between the product and the parasitic masses stated.

- 24 In particularly critical applications such as products of low density, or measuring through thick tank insulation layers, for the purpose of suppressing parasitic masses it may be necessary to use four sensor-internal gravimeter circuits. Since the described measuring method selectively analyses the gravitational fields in the direction of the measuring straight, parasitic masses whose centre of gravity is not spatially located on the measuring straight are taken into account in the measuring process either in a reduced manner or not at all. Secondly, below, a description follows of the method according to the invention of measuring continuous fill levels by analysing the intrinsic gravitational field of the product. Measuring continuous fill level values can take place by means of four different methods of field analysis. These methods can be used individually or in combination in a sensor. Fig. 7 shows a diagrammatic cross-sectional view of a partly filled product tank on which five different types of continuously measuring sensors according to exemplary embodiments of the present invention have been installed. The first method is based on the analysis of the field intensity difference in the case of product being present between the gravimeters. For this purpose, preferably a first gravimeter is installed on the underside of the product tank and a second gravimeter on the top of the product tank. In Figure 7 this sensor type is designated 701.

- 25 If the tank is empty, a measuring value difference between the two gravimeters occurs which corresponds to the earth field gradient multiplied by the height of the tank. This value is removed from the measuring result by means of null balancing. If the tank is filled, the gravitational field of the product in the location of the bottom gravimeter acts against the earth field so that the measured field intensity of said earth field decreases. In the location of the upper gravimeter, the product field is added to the earth field, so that its field intensity increases. After suitable measuring-value linearisation, the measured field intensity differential between the two gravimeters results in a product level display that is proportional to the product mass in the tank. It is also possible to affix the two gravimeters on two opposite lateral walls of the product tank. However, from the point of view of accurate acquisition of the empty state and the full state, the previously mentioned installation type is preferable. The measuring result depends on the product density. The second method is based on the analysis of the reduction in the field strength as the distance to the product increases. According to the law of gravitational fields, the gravitational field outside the product decreases with the reciprocal value of the distance square to its mass centre. The degree of distance-related change in the field intensity is both a measure of the product diameter and of the distance to the product. A sensor that operates according to this principle comprises several gravimeter circuits installed on a line. The installation line - 26 preferably points towards the centre of gravity of the product. In Figure 7 this type of sensor is designated 702. Sensor 702 comprises, for example, five gravimeter units 708, 709, 710, 711 and 712, which are arranged vertically one on top of the other. The sensor can be mounted either on the tank or underneath the tank. Furthermore, the sensor comprises a communication interface 713 which, for example, comprises a transmitter. By way of the communication interface 713, data records which, for example, are based on measuring data of the gravimeter units 708, 709, 710, 711 and 712 can be transmitted by radio transmission 716 to an external analysis unit 715 with a receiver 714. Of course, it is also possible to integrate the analysis unit 715 in the sensor, and then for example to transmit an analysis result (e.g. fill height) by way of the interface 713 to an output unit or to a device for further processing. By means of the measured field values and the known physical laws of distribution of gravitational fields outside mass bodies, the sensor signal processing device computes the distance from the product, or the height of the product. If a total of only two gravimeters are used, only two field measuring values that are differently spaced apart from the centre of gravity of the product are available, from whose difference only one field gradient can be calculated. Consequently, the fill-level measuring value that can be derived from said field gradient depends on the density of the product. Therefore it is preferable to use at least three gravimeters from whose field measuring values at least two field gradients from different locations can be calculated. From these field gradient values, of which there are at - 27 least two, the fill level can be determined irrespective of the density. For the measuring problem to be solved, the three parameters of fill height, product density and far field amplitude, which parameters are unknown in this case, require at least three gravimeters that furnish three field measuring values from different locations. When the sensor is first commissioned, null balance is to be carried out with the tank empty, so as to remove static near-field components, such as the empty mass of the tank, from the measuring result. The third method is based on the analysis of the field intensity distribution within the product or along its delimiting surfaces. According to the law of gravitational fields, the field generated by a spherical product increases in a linear manner from the mass centre to the product surface, with the field strength within the product being proportional to the centre of gravity distance. If the product is not spherical in shape, the ratios are more complex but nevertheless strictly subject to the laws of physics. Generally speaking, at the centre of gravity of the product, its intrinsic field intensity is zero. The sensor 703 comprises several gravimeters 718, 719, 720, 721, 722, installed on a line, which gravimeters 718, 719, 720, 721, 722 are located in a shared protective tube. The sensor is installed such that it is preferably immersed in the product, but said sensor can also be affixed so as to be perpendicular in relation to the lateral wall of the tank. If in the case of an immersed sensor 703 the installation line of the gravimeter leads through the centre of gravity of the product, this is particularly advantageous without in any way being mandatory.

- 28 By means of the field-intensity differential between the individual gravimeters, and by means of the known physical field distribution laws within mass bodies, the sensor signal processing device computes the fill level value. By means of carrying out null balancing, static near-field components are compensated for. If only 2 gravimeters are used, the fill-level measuring result depends on the fill level density. If at least three field measuring values from different locations are available, the fill level can be determined so as to be independent of the density. The gravimeters of the sensor, which gravimeters depending on the fill level are not immersed at the time, can additionally be used for determining the fill level according to method two. Likewise it is advantageous to offset the value of the last immersed gravimeter against the value of the first no-longer-immersed gravimeter according to method one. By combining the resulting values from all the methods used, the measuring accuracy of the sensor can be enhanced. This sensor type provides an advantage when compared to immersed fill-level rod sensors involving other physical measuring principles in that the sensor can measure through a separation tube that is installed in the tank, which separation tube protects the sensor from the product. In this way, slide-in sensors for transport tanks can be provided. A separation tube, closed on one side and open towards the outside, is installed in the tank. During filling and for other checking purposes, the gravitational sensor is temporarily slid in and measures the fill level through the separation tube. In this arrangement the tank remains hermetically sealed. The example of Figure 7 includes such a separation tube.

- 29 The fourth method is based on an analysis of the spatial position of the gravitational-field vector. In Figure 7 such a sensor is designated 704. If for reasons associated with the installation, in a sensor 704 the individual gravimeter positions are not situated on the rising straight of the centre of gravity of the product, then in the case of changes in the level of the product the gravitational-field vector acting on the gravimeters not only changes its length but also its spatial orientation. The three-dimensional gravitational-field vector is formed by the orthogonal field components in the x-, y- and z directions. The z-field points in the direction of the fill height and is perpendicular in relation to the ground. In contrast to this, the x- and y-fields extend parallel in relation to the ground. In this arrangement the x-field represents the gravitational component in the direction towards the middle of the tank, while the y-field represents the component parallel to or tangential to the tank wall at the location of the installation of the sensor. If the sensor 704 is installed in the middle on the lateral wall of a symmetrical tank, then when the tank is being filled, the gravimeters register a field in the x- and z directions. No y-field component occurs because, due to the sensor installation in the middle, the individual y-fields at the sensor location cancel each other out. In the case where the installation is not in the middle, the product generates all three field components at the gravimeter positions. The amplitude ratios of the orthogonal field components on the gravimeters, or the angular orientation of the resulting gravitational-field vector in space, are/is characteristic in relation to each individual fill level value, and consequently the fill height can be - 30 derived therefrom. Since the amplitude ratios are analysed, the absolute amplitude values are not input into the measuring result so that said measuring result is independent of the product density. Each gravimeter in the sensor 704 determines the components of the gravitational field in the three spatial dimensions. By differential value formation between the gravimeters, fluctuating far-fields are removed from the field intensity values obtained in this way. Null-balancing at the time of commissioning the sensor is used to eliminate the static surrounding gravitational field. From the differential field intensity values obtained in this way and from the known positions of the gravimeters, the sensor-signal processing device computes the position of the product and thus the fill level value. Depending on the design of the sensor 704, this fourth method, too, can be combined with the other three methods. The sensor which in Figure 7 is designated 705 and which comprises two gravimeter units, which sensor is installed on the lateral wall of the tank, uses, for example, the methods one and four. Apart from computing the fill height from the gravimeter measuring values by applying the known field distribution laws of physics, taking into account the installation positions of the gravimeters and any additionally input tank data, there is also the option of determining the fill height from the gravimeter measuring values at the time by a comparison with previously stored gravimeter measuring values obtained at the time of filling during commissioning. For this purpose, after the sensor has been installed, the tank to be measured is filled step-by-step, and after each filling step the fill level at the time is communicated to - 31 the sensor. In relation to this input fill level value, said sensor stores the occurring gravitational measuring values of all the gravimeters. During subsequent measuring operation the sensor-signal processing device then compares the actually-measured gravitational values with the stored support values and interpolates the fill level between the two nearest stored values. In the methods 2 to 4, it is preferably not the absolute sizes of the field-differential measuring values but instead the ratio values of the individual field differentials among each other that are compared. In this way even products with a density of the medium which density differs from that of the product used at the time of filling during commissioning are measured accurately. By applying several of the methods 1 to 4 in a sensor, the fill level can be determined multiple times according to various methods. Averaging the individual measuring results leads to enhanced measuring accuracy of the sensor. When a parasitic mass is encountered, the individual methods react with different sensitivities, depending on the position of the mass. Averaging several methods thus additionally enhances the insensitivity to parasitic masses. It is also possible, after carrying out a plausibility check of the individual measuring results, to exclude from averaging any result that has been recognised as being inaccurate. By using a greater number of gravimeters and thus field intensity measuring points in a sensor than is theoretically required, it is also possible to over determine the fill level. Moreover, additional gravimeters provide the option of reducing the distance between field - 32 measuring points so that the near-field measuring range of the sensor is reduced in size, and any parasitic masses act rather in the way of unproblematic far fields. Selecting a favourable position to install the sensor on the product tank additionally enhances interference robustness. Apart from these passive methods of suppressing the influence which parasitic masses have on the measuring result, there is also the option of determining the parasitic mass in a targeted manner and to subsequently calculate it out of the end result. An adequate number of field measuring values and thus input values for the correction algorithm is a prerequisite for this approach. The number of the gravimeters required in a continuous fill level sensor also depends on the shape of the tank. Slim and irregularly formed tanks may require a greater number of gravitational measuring points and thus gravimeters than do simple flat tanks. In the sensor designated 704 in Figure 7 the gravimeters are surrounded by a shared metal tube. The sensor is thus only suitable for installation on straight tank walls. If the gravimeters are integrated in a flexible tape, the sensor can also follow curved tank walls. Apart from these preassembled sensors, individual gravimeter units can also be affixed to the tank wall at regular spacing and can be connected, by way of a two-conductor bus cable, to the analysis electronics of the sensor. The individual gravimeters are preferably connected, by way of cable penetration technique, to a rubber-like flat ribbon cable of rectangular cross section. The continuous bus cable thus does not require any cutting or stripping.

- 33 In the case of sensors comprising a small number of gravimeter units, such as type 701 and type 705 in Figure 7, it is also possible to use an existing field bus for data exchange. All the units are connected to each other by way of the field bus. The slave units transmit their measured gravitational values directly to the bus; the master unit reads these values from the bus, offsets them against its own gravitational measuring values relating to the fill level value, and outputs this value to the bus. On the basis of the miniature gravimeter circuit described later and on the basis of modern radio transmission methods, the development and application of gravimeter units that transmit wirelessly is also possible. Such devices comprise, for example, the gravimeter circuit, a highly-integrated radio interface, and a long-life lithium battery as a power supply. The volume of this unit is equivalent to that of a match box or even smaller. The required number of gravimeter units are glued to the corresponding positions on the tank. A remote analysis unit receives the measuring data of all the gravimeters and offsets this data against the fill level value. In this arrangement one analysis unit is enough to receive the data of a multitude of tanks and to calculate the fill levels of these tanks. Still further-reaching miniaturisation is possible by means of technologies as used in smart credit cards and goods labels. In this way the gravimeter units can be designed as flat, pliable stickers. The interior of such a gravimeter unit comprises the gravimeter chip, the transmitter chip, a planar antenna, a lithium polymer battery, and if necessary an amorphous solar cell to charge the battery. The surface is, for example 1 cm by 4 cm, with the thickness being approximately 1 mm. With these sensory stickers it is then possible to instrument tanks and pipelines in a - 34 revolutionary simple manner. A central receiver unit then calculates all the fill level values and outputs them to the process control device. If by means of special gravimeters it is possible in one gravimeter unit to measure several gravitational field intensities in various locations or to determine their differential value directly, then the above-described gravitational-field measuring point arrangements and the associated gravitational-field analysis methods apply analogously to such gravimeter units without thereby leaving the scope of the invention. Fill level measuring on the basis of gravitational fields provides the following characteristics and application advantages: All liquids and liquid gases can be measured. Bulk materials must have a minimum density, but granulation is of no consequence. Measuring can take place through the closed tank wall, with all wall materials being suitable. This is particularly advantageous in the case of corrosive, abrasive, explosive, sterile, toxic, bio-hazardous, radioactive or ultra-pure products, as it is in the case of high-pressure tanks. Very hot or very cold products are measured through the tank insulation. Since the measuring method reacts to mass quantities, product adhesion, dirt deposits or foam are ignored. The measuring method is thus suitable also for particularly sticky and viscous products. Products that tend to be subject to strong electrostatic charging can neither damage the sensors that are installed on the outside wall, nor can they affect said sensors with product. Application in potentially explosive areas poses no problem. No energy is coupled into the product. Sensor current supply and measuring value transmission are - 35 possible by way of an intrinsically safe 4...20 mA current loop. Components built into the tank, for example agitator blades, baffle plates, wash plates, heating- and cooling coils, heat-exchanger damper plates, perforated false floors, gas injector lances, catalyst support plates and packed beds are penetrated unchanged by the gravitational field so that the product located behind and below is measured without any problems. Apart from being installed on the outside wall, gravimeter sensors can also be screwed into or flanged onto the tank wall. In this case, certain sensor designs finish so that on the inside they are flush with the wall, in this way preventing any narrowing of the discharge cross section of tanks or of the through-flow cross section of pipelines. Small screw-in threads size M8 are possible. Sensors that are installed on the outside of the tank can be replaced or retrofitted without this requiring any interruption in the operation of the plant. Below, the design of a novel miniature gravimeter according to the invention is described, as shown as exemplary embodiments in Figures 1 to 5, which miniature gravimeter is particularly advantageously suited to be used in industrial plant sensors. The technology used in conventional precision-mechanical gravimeters as used in the field of geology is not only far too expensive for applications in industrial measuring, with the response time being too slow, but the far-too large design volume of such devices is also a particularly unwelcome aspect. This excessively large design volume not only prevents the implementation of a compact sensor, but it also does not allow the required point-shaped gravitational field determination at close spacing.

- 36 Conventional gravimeters are associated with a further disadvantage in that they can only measure the gravitational field in one spatial direction. A three dimensional field determination thus requires three such devices. Apart from its immense expenditure, such a configuration would not make it possible to measure the three field components at the same spatial point. Integrated micromechanical acceleration sensors represent a clear step in the right direction. In these sensor elements, by means of an etching process, a bending-beam structure with a mass element formed to it is produced from a silicon substrate. By means of capacitive distance sensing the excursion of the bending beam is acquired, and by means of an electrostatic compensation force field the zero position of the bending beam is restored. The measuring result is obtained from the required compensation field intensity. These sensor elements are associated with a disadvantage in that they do not achieve the accuracy and resolution that is required for measuring gravitational fields. The spring constant of the bending-beam structure cannot be reduced at will because otherwise instances of plastic deformation occur, which result in a loss of zero-point stability. Furthermore, complex micromechanical structures are generally subject to a host of error influences. There is a further disadvantage in that the mechanical component and the electronic component have to be produced on the same material substrate, and consequently neither of the two components can be produced in an optimal manner. For three-dimensional field measuring, in this case too, three measuring elements that are affixed orthogonally in relation to each other are required.

- 37 According to the invention, the implementation of a cost effective miniaturised high-resolution gravimeter measuring cell takes place in that the gravity-field detecting mass element is kept afloat in a contactless three-dimensional manner by means of electrostatic force fields. There is thus no necessity to provide a mechanical spring element. The position of the mass element is determined capacitively. The floating mass element is preferably arranged directly above an integrated semiconductor circuit so that at least part of the required field-generating and measuring electrodes can be affixed directly on said semiconductor circuit. From the electrical field intensities required to maintain a defined floating position of the mass element, the values of the gravitational field intensities in the spatial directions can be calculated. Figures 1 and 2 show a first exemplary embodiment of such a floating-body gravimeter cell. Fig. 1 shows a cross section of an exemplary embodiment of a gravimeter unit according to the present invention. Fig. 2 shows a top view of a semiconductor chip, with electrodes affixed thereon, of the embodiment shown in Fig. 1, of the gravimeter unit according to the invention. On a semiconductor chip 101 which comprises the signal processing electronics, a formed piece 102 is fastened, which comprises two conical indentations. The formed piece 102 comprises a non-conductive insulation material, for example glass or ceramics. In each of the two hollow spaces created by the indentations there is a conical metallic body 100, 200. Its diameter is, for example, 0.5 mm. In order to be able to let electrostatic forces act on said metallic body 100, 200 in all three spatial directions, in - 38 the interior of the hollow space eight electrodes are installed, each electrode having the shape of a quarter circle segment. One half thereof is situated on the semiconductor chip 101, thus forming the base electrodes 113, 213, 1, 2, 3, 4, 201, 202, 203, 204, while the other half is plated-up, on the formed piece 102, on the inside of the conical indentation, thus forming the lateral electrodes 115, 116, 215, 216. On the underside of the formed piece, the lateral electrodes electrically contact the chip 101 by way of the contact faces 117, 217. The reference characters 118, 119, 120 designate product material. Figure 2 shows the chip surface with the base electrodes and the contact surfaces 5, 6, 7, 8, 205, 206, 207, 208 to the lateral electrodes. The gap 108 between the floating bodies 100, 200 and the chip 101 or the formed piece 102, which is shown in Fig. 1, acts as a dielectric to the electrical field. The dielectric 108 consists either of a vacuum, an inert gas such as nitrogen, or a non-conducting liquid, preferably of high dielectric permittivity. Apart from the values of the capacitances and electrical field forces, which values have been increased by the dielectric permittivity, the use of a liquid also provides the advantage of good damping of mechanical vibrations as a result of liquid friction due to viscosity. The gap width is narrow, for example 0.005 mm. As a result of the application of a voltage between the base electrodes 113, 213, 1, 2, 3, 4, 201, 202, 203, 204, the floating body is electrostatically drawn downwards. A voltage between the lateral electrodes 115, 116, 215, 216 draws the floating body upwards. If on one side a voltage is applied between a base electrode and a lateral electrode, the floating body is drawn to the corresponding - 39 side. By suitable electrode control, rotary tilting moments can also be generated. Either direct voltage or alternating voltage can be used for the coupling-in of the electrostatic forces. Capacitive distance sensing for determining the precise position of the floating body is preferably carried out by way of the same electrodes that are also used for force coupling-in. It should be noted that the high-frequency measuring field also generates attraction forces. The measuring- and closed-loop control electronics on the semiconductor chip then ensure that the floating body is held in a precise symmetrical position in relation to the electrodes. The gravity acting from the outside through the gravitational field onto the floating body is cancelled out by a counter-directed electrostatic compensation force. The required compensation force in the three spatial directions is thus a measure of the gravitational field in the three spatial directions. The applied drive voltages of the individual electrode segments are preferably selected such that an average mass potential results at the floating body. For this purpose one half of the electrodes is driven at a positive voltage level in relation to the average mass, while the other half is driven at a corresponding negative level in relation to the average mass. Since the floating body integrates the effective electrostatic forces over time, apart from analog drive voltages, digital pulse-width-modulated binary- or ternary level voltages can also be used. Below, the physical calculation equations for an idealised floating-cone gravimeter are stated. Furthermore, by means - 40 of a calculation example the level of electrode drive voltages for gravitational-field compensation experienced in practical application is shown, as are the resulting electrode capacitance values. Lifting force and effective weight of the floating body: n=p,-V V=-.d2.h m= pI -d -h 12 12 FA = p 2 V9 =P 2 - '-d2 -h-g 12 FG=(p -p 2 )- '&=(P -P 2 ).'--2 -h-g 12 m = cone mass d = cone diameter h = cone height V = cone volume pi = cone density P2 = dielectric density g = gravitational field intensity FA = lifting force FG = effective weight Electrostatic forces FEL Of the individual electrodes: F -A -,-A -U 2 2S 2 Eo = electrical field constant -S.85 -10-"Fi1 - 41 = dielectric permittivity of the dielectric A = effective electrode surface in relation to a spatial direction x, y or z U = voltage between the electrode and the floating body s = dielectric gap width h-lI 3600 A =A, I =d-sin-- 2 2n h . 1800 A =A,=--d-sin 2 n Insulating surfaces between the A =d2 electrodes have not been taken into account n = number of the base electrodes or lateral electrodes 1 = chord length of the lateral electrodes x, y = spatial direction parallel to the base electrodes z = spatial direction perpendicular to the base electrodes FEL=(x) = 2 0 hdU' sin - 8sm 4s 2 n Value for one electrode segment co-s,-td 2 -U2 17:L (Z)

-

o.r 7~ 2.U 8n-S2 Electrode drive voltage for compensating the weight or gravitational force FL = FG - 42 * d U 2 -sin 1800 =(pI-p 2 ).- d2-h-g, 4s' n 12 U" =. - 8 - P2)- -d Applies analogously to Uy

.

;,- , i 180" n with gy Ux = drive voltage of a lateral electrode to compensate for a gravitational field in x-direction c, -Er -n-d 2-.U 2 2 S2 (PI -P2) dA h-g, 8s- 12 U= -g 2 (p -P 2 )h U, = drive voltage of all base electrodes or all lateral electrodes to compensate for a gravitational field in z direction Capacitances between electrodes and floating bodies: CB = capacitance of a base electrode Cs = capacitance of a lateral electrode As, AB = surfaces of the electrodes E -* .A T-d 2 n-d d2 2 C= AB = As- -- +h s 4-n 2-n 4 B = .*,- d 2 = C = *,n d* 4+h2 4-n s S 2.n-s 4 - 43 Calculation of gravitational field m 4 4 g=7- m=p-V V=--T-r 3 g=y-p---r r 3 3 g = gravitational field at the surface of a spherical object y = gravitational constant = m = mass r = sphere radius V = volume p = sphere density Application example The gravimeter is laterally installed on a spherical tank. The point of the cone points downwards. The product field acts in x-direction. The earth field acts in z-direction. The product is water. Given values: Product density p = 1000 kg/M 3 Tank radius r = 0.5 m Cone diameter d = 500 pm Cone height h = 250 pm Cone density pi = 2700 kg/M 3 Dielectric density P2 = 700 kg/m 3 Gap width s = 5 pm Electrode number n = 4 Dielectric permittivity Er = 20 Earth field gE = 9.81 m/s 2 Calculated values: Base electrode capacity CB = 1.74 pF Lateral electrode capacity Cs = 2.46 pF - 44 Product gravitational field gF = 2.4910- r/s 2 Drive voltage for the base electrodes U, = 680 mV Drive voltage for the lateral electrode pointing away from the product Ux = 171 pV As the calculation example shows, low voltages are sufficient to generate the electrostatic compensation forces, so that operation of the measuring cell electronics on a standard 5 volt supply voltage is possible without any problems. Since the floating-cone gravimeter due to its design does not contain a mechanical spring component, not only are there are no error components that such a structure would entail, but there is also no longer any restriction, due to spring stiffness, in relation to the measuring value resolution. During the measuring procedures, the components of the gravimeter cell are advantageously not subjected to any deformation but are operated in a purely static manner. There are therefore no changes in component dimensions as a result of creep action or parameter-changing material recrystallisation processes as a result of mechanical tensile strain or compressive strain. Due to the fact that no mechanical structures have to be produced on the semiconductor chip, its manufacturing process can be designed entirely with a view to optimising the electronic circuit components. If a liquid is used as a dielectric, then the thermal expansion of this liquid has to be taken into account. Within the formed piece it is, for example, possible to provide a partly gas-filled capillary tube into which the dielectric liquid can expand. Due to the surface tension of - 45 the liquid, as is the case in a liquid thermometer, creeping of the gas column from the capillary is prevented. In the case of a gaseous dielectric, the floating-body void is preferably designed so as to be hermetically sealed so that when there is a change in temperature the volume and thus the density taken up by the gas remain constant. Since the gravimeter measuring cell has to meet the most stringent requirements as far as measuring accuracy is concerned, various error compensation mechanisms are used. It is above all a matter of compensating for temperature related and age-related changes in values of a mechanical and/or electrical type. In order to generate two measuring values that mathematically depend in a different way on the gravitational field and the error components, two floating body units of identical dimensions can be installed on the chip. Likewise, the associated drive circuits and analysis circuit components can be designed so as to be identical. There is a difference between the two arrangements in that the floating bodies 100, 200 (see Fig. 5) are made from two different metals of different density. This results in the gravitational field entering the measuring results of the two floating-body units with two different factors. Since both factors are known, by offsetting the two measuring values, error compensation can be carried out. If a liquid dielectric is used, the lift error generated as a result of the thermal expansion of the dielectric can be compensated for in this manner. A comparison of the capacitance values of the eight electrode segments within a floating-body unit provides additional correction values.

- 46 While a change in the position of the floating body results in an increase in the capacitance in part of the electrodes, and a decrease in the other part, thermal material expansions result in the same type of changes. By suitable offsetting of the electrode segment values among each other, these errors can be compensated for. By means of a further hollow space arrangement that does not comprise a floating body, it is also possible to separately measure the base capacitance values. By generating test forces, further information about the function parameters of the measuring cell can be obtained. To this effect an additional electrostatic force field is coupled into the floating body by way of the existing electrodes. This causes the field regulation in the electronics to adapt the intensity of the existing compensation field so as to maintain the force equilibrium in the floating body. With this method the characteristic of force field generation can be measured through. By changing the floating-body position from the centre, due to other desired-values specified for closed-loop control, on the basis of the resulting electrode capacitance values at different spacing between the floating body and the individual electrodes, the capacitance-spacing characteristic of the measuring cell can be measured again. With this method all three dimensions of the cell can be automatically measured and recalibrated. Direct temperature compensation represents a further error correction option. On the semiconductor chip a temperature sensor is also integrated and compensation is carried out according to predetermined value dependencies. Since the entire measuring cell itself is only the size of a chip, no compensation-falsifying temperature gradient occurs.

- 47 In the case of an identical type of residual error of the cells, the offsetting procedure of the measuring values of the individual gravimeter circuits, which offsetting procedure is carried out in the complete sensor, results in a further compensation effect. The chips for the measuring cells of a sensor should therefore be taken from the same production wafer. If despite all the correction measures and the advantageously high degree of integration of the measuring cell the required measuring accuracy is not achieved, by using a third floating body with a third density value, a further data record of input values can be generated to enhance the accuracy. Figures 3 and 4 show a further exemplary embodiment of a floating-body gravimeter arrangement. Fig. 3 shows a cross section of a further exemplary embodiment of a gravimeter unit according to the present invention. Fig. 4 shows a top view of a semiconductor chip with electrodes affixed thereto of the exemplary embodiment of the gravimeter unit shown in Fig. 3. If the gravimeter cell is always installed so that the earth's gravitational field points away from the chip surface, the entire electrode structure can be affixed to the chip 101. The formed piece 102 then does not need any electrical connections. By means of the outside electrodes 114, 214 forces can be generated that act laterally on the floating body 100, 200. For reasons connected with installation, the force component towards the chip surface, which force component is always also present in this arrangement, acts against the earth field.

- 48 Since the outside electrodes can only generate small forces, the floating body 100, 200 can advantageously be designed as a flat disc with little mass. By combined driving of the outside electrodes 114, 214 and the inside electrodes 113, 213 all the required force components can be generated. In this arrangement the formed piece 102 can be made either from an insulating material or from metal. If a metal formed piece is used, said formed piece is connected to the circuit mass potential, thus at the same time acting as an electrical shield for the measuring system. The cell alignment towards the earth's surface can deviate by approximately +/- 45 degrees in both spatial directions. Apart from generating the described electrostatic attraction forces, it is also possible to generate repelling forces. To this effect the floating body 100, 200 needs to comprise a non-conductive material, such as glass or ceramics. The dielectric permittivity of said material must be lower than that of the liquid used. An electrical field created between two electrodes then has a repelling effect on the floating body. Combined generation of both types of force is possible in that the non-conducting floating body comprises part metallisation. In this way the semiconductor chip is in a position, with the electrodes situated on it to attract the metallised part of the floating body while repelling the non-metallised part. It is thus possible to generate forces in all spatial directions so that there is no need for any cell alignment. While with the use of attracting electrostatic forces, closed-loop control of the electrode voltage is mandatory in order to keep the floating body afloat in a stable - 49 manner, with the use of repelling forces in principle no closed-loop control of the force field is required. In the case of a diminishing distance and thus increasing electrical field intensity, approximation of the floating body to a repelling force field results in an increase in the field forces. The floating body therefore only approaches the electrodes until the gravitational forces and the electrical field forces are balanced. From the resulting spacing of the floating body to the individual electrodes, the value of the gravitational field can then be calculated in the three spatial directions. However, the application of active closed-loop field control in the case of repelling force fields can still be favourable because a constant floating-body position provides advantages in error compensation. Figure 5 shows a third exemplary embodiment of a floating body gravimeter arrangement. In this arrangement, too, the formed piece 102 does not need an electrode structure. It is possible to couple-in forces of either polarity in all three dimensions onto the floating bodies 100, 200. There is a difference when compared to the arrangement described above, in that purely metallic floating bodies can be used. To this effect the formed piece 102 is in principle designed so as to be conductive and is connected to mass. By special mechanical shaping, said formed piece 102 is imparted with the function of an electrode that attracts the floating body. This is achieved in that the effective electrode surface is reduced to a ring-shaped rim zone 112, 212 by providing the indentation 111, 211. The surface of this rim zone 112, 212 is smaller than the cumulative surface of the inside electrodes 113, 213 and the outside electrodes 114, 214 on the chip. It the chip electrodes 113, 114, 213, 214 are driven at an identical voltage value, which differs from mass, then a higher - 50 electrical field-line density results on the ring electrodes 112, 212 than on the chip electrodes 113, 114, 213, 214. Consequently the floating body is attracted by the ring electrode. If the floating body is to be attracted by the chip electrodes, this is achieved by using different voltage potentials between the individual chip electrodes. Fig. 5 also shows an alternative embodiment of the floating bodies 100, 200. In order to increase the lateral forces that can be generated electrostatically, each of the floating bodies 100, 200 comprises an indentation 115, 215 on its underside. In this way a ring-shaped rim zone 216 that is opposite the chip electrodes 113, 114, 213, 214 is created. The rim zone 216 comprises an additional inside lateral surface 219 which makes it possible for the inside electrodes 113, 213 to also couple lateral forces into the floating body. The outside lateral surface 218 is used by the outside electrodes 114, 214 to couple-in lateral forces. There is also the option on the underside of the floating body to provide several concentric ring structures, each comprising its own associated set of inside- and outside electrodes, so as to be able to generate even greater lateral forces. By suitable driving of multiply-present electrode segments, the electrode surface that is electrically active to generate the force field can be varied for test- and monitoring purposes. Furthermore, there is the option of implementing the ring structures at different heights so that each individual ring is differently spaced apart from the electrodes on the chip surface. Such an arrangement makes it possible to multiply determine the floating-body position with the use of various gap widths. By means of the known height values - 51 of the rings, it is possible to remove existing error components from the distance sensing values that vary according to the difference. When compared to a variation in the desired position value, for the purpose of measuring the capacitance-distance characteristic, this method provides an advantage in that there is no need to move the floating body. Furthermore, the electrodes associated with the individual rings make it possible to variably couple-in the electrical field forces across different gap widths. As a fourth exemplary embodiment, Figure 8 shows a gravimeter with a gap-width-structured floating body 109, which comprises three ring units a, b, c. The ring units comprise ring structures 116a, 116b, 116c and indentations 115a, 115b, 115c. Ring-shaped outer electrodes 114a, 114b, 114c and inside electrodes 113a, 113b, 113c are affixed on the semiconductor chip 101. If a gaseous dielectric of a density that is kept constant is used, in such a design there is the option of deriving all measuring values that are required for error compensation from a single floating body. In this case, as shown in Figure 8, the gravimeter measuring cell only requires a total of one floating arrangement. If a liquid dielectric is used, its thermal expansion and the resulting error in lift, generally speaking, requires two floating arrangements for error compensation. However, if in the dielectric used, the density value can be calculated from its dielectric permittivity, for example because the electrical susceptibility of the dielectric is proportional to the density value, then in this way it is also possible to carry out lift-error compensation.

- 52 The determination of dielectric permittivity takes place by offsetting the capacity values of an adequate number of electrodes so that other capacity-determining values, for example the floating-body position and the substrate base capacitances, can be eliminated. To this effect an arrangement as shown in Figure 8 comprises a sufficient number of electrodes. If angular instead of round floating bodies are used, accordingly, the above-mentioned ring structures are analogously to be replaced by bodies comprising polygon like structural geometries. Apart from being made of metal, as an alternative electrically conductive floating bodies or formed pieces can also be made from a metallised insulation material such as glass or ceramics. Dimensionally accurate production of metallic floating bodies or metallised formed pieces can take place by stamp-forming suitable blanks. Components based on glass can be precisely formed by being pressed in their plastic hot state. Apart from solid floating bodies, in principle it is also possible to use liquid spheres. The dielectric can either be gaseous or it can comprise a non-miscible second liquid. Likewise the use of a gas bubble that is electrostatically kept afloat in a liquid is imaginable. The strongly rising surface tension at small dimensions ensures that these floating objects have a defined form. It is also possible to surround the floating body entirely by a formed piece arrangement that carries all the electrodes, and to couple the semiconductor chip or other electronics by means of conductor connections. Likewise it is possible to embed the floating body in a sandwich-like manner between two semiconductor chips. Moreover there is the option of providing the indentations for the floating - 53 body on the semiconductor chip itself, rather than in the formed piece. In this regard Figure 9 shows a fifth exemplary embodiment of a floating-body gravimeter, wherein for the sake of simplicity only one floating arrangement is shown. In the interior of two formed pieces 91, 92, joined at a separation line 93, each of which formed pieces 91, 92 comprises a hemispherical indentation 10, there is a spherical floating body 100. Each of the formed pieces 91, 92 in its indentations 10 comprises, for example, four electrodes in the shape of quarter-sphere domes in order to be able to couple force-generating and distance-measuring electrical fields into the floating sphere 100. Of the four electrodes to each formed piece, Fig. 9 only shows two electrodes 5, 8 or 6, 7. Reference character 94 designates an electrode expansion limit. Reference character 95 designates an insulation gap. The spherical shape of the floating body 100 makes possible simplified closed-loop field control because, due to the rotational symmetry of the spherical body in relation to all three spatial axes, there is no need to provide closed loop control of all three rotatory degrees of freedom, and therefore only the remaining three translatory degrees of freedom require closed-loop control. Since both formed pieces 91, 92 generally-speaking are of a passive nature and therefore have to be connected to external electronics by means of a conductor connection with stray capacitance, floating arrangements with an electrode-bearing semiconductor chip are particularly advantageous. In the floating-body gravimeter, particularly preferably electrical fields are used for force generation and distance sensing. They can be generated with minimum energy - 54 expenditure, they are simple to shield, and the required electrode arrangements can be produced economically and with great precision, and they are able to be integrated. As an alternative it is also possible to use magnetic fields. For this purpose the floating body is surrounded by electromagnetic coils. A floating body made from a ferromagnetic material such as iron or ferrite ceramics is attracted by the magnetic field of the coils. Depending on the field polarity of the coils, bodies made of a permanently magnetic material can be either attracted or repelled. Due to eddy-current formation by alternating magnetic fields of the coils, bodies made of non-magnetic but electrically conductive material such as aluminium, can be repelled by said coils. Distance sensing, too, can take place by means of magnetic fields. From the inductance values of the coils, and from magnetic coupling between the coils, the distance from a ferromagnetic floating body can be determined. In the case of an ohmically conductive body distance sensing can take place by analysing the resistive component of the alternating current impedance of the coils. Fields emanating from the floating body, or field amplitudes changed by said body, also provide a measure indicating the distance. Field intensity measuring can, for example, take place by means of magnetoresistive hall sensor or GMR sensor elements. If magnetic methods are used, adequate shielding of the measuring cell from surrounding magnetic fields must be provided. The floating-body position can also be determined conductively. To this effect an ohmically conductive dielectric is to be used. The resistance value that then occurs between individual conductive measuring electrodes - 55 provides a measure which indicates the floating-body distance from the electrodes. If a dielectric is used whose resistance is not too low, simultaneous resistive and capacitive distance sensing can be carried out. Likewise the option of electrically generating force fields remains. Furthermore, optical distance sensing is also possible. This can, for example, take place by analysing the shading effect which the floating body has on a beam of light, by means of measuring the amplitude of light from a point light source, which light is backscattered by the body, and it can also take place interferometrically. In principle, there is also the option of mechanically for example by having a fluid stream pass or stream around the floating body, which fluid is used instead of the dielectric, or which fluid can be the dielectric - coupling forces into the floating body, as well as from the gap width-dependent flow resistance of the arrangement to draw conclusions relating to the body's position. Various options exist to suppress the parasitic influence which vibrations from the surroundings have on the gravimeter output signal. It is advantageous to embed the measuring-cell carrier in the insulation material, or with other measures to inhibit vibration transmission from the sensor housing to the measuring cells. Furthermore, with the use of a liquid dielectric the liquid friction that is caused by the flow can be used to suppress vibration. In the case of measuring cells with a gaseous dielectric, by means of a corresponding design of the floating body and - 56 the formed piece it is also possible to achieve vibration damping by way of the dielectric. To this effect the floating body is designed such that in the case of movements in any of the three spatial directions it causes the largest possible volume displacement of the gaseous dielectric, while at the same time it has only a minimum intrinsic weight. For this purpose the floating body 100 can be designed in a cup-shaped, hat-shaped or semi-closed cylindrical design as shown in Figure 8. Designs as completely-closed hollow bodies are also possible. The gas volume, which is displaced during movement, must flow out, through the narrow gap between the floating body and the formed piece, to the opposite side so that only slow movements are possible. However, in the case of metallic floating bodies, as an alternative it is also possible to use eddy currents for vibration damping. To this effect a permanent magnet is affixed to the formed piece, which permanent magnet subjects the electrically-conductive floating body to an inhomogeneous magnetic field. Each movement of the floating body leads to the formation of eddy currents, whose own magnetic fields, in accordance with Lenz's law, act against the movement that causes them. There is also the option of compensating for vibration forces in real time by means of electrostatic forces of the electrodes. Since mechanical vibration usually occurs in the frequency range of 1 to 1000 Hz, but closed-loop control of electrostatic fields can take place at frequencies of several 100 MHz, electrical compensation forces are faster by more than five powers of ten than the highest mechanical vibration frequencies.

- 57 Since vibration represents a pure alternating value, while the gravitational field is a constant field value, the desired separation can be brought about by vibration suppression and measuring value integration. As a result of the extensive diagnostic functions within the context of error correction, the floating-body gravimeter cell represents a self-monitoring measuring system. In the case of a failure the sensor operator receives a reliable fault message, and similarly, in the case of parameter deterioration, a preliminary failure signal can be output as a warning message. Due to the extremely small nature of the measuring cells, for particular safety requirements it is also possible to construct fully-redundant sensors without this resulting in an increase in the external dimensions. Due to the principles involved, the measuring cells or the complete sensors do not influence each other. By arranging a multitude of measuring cells in the form of a matrix, the implementation of image-generating sensors is also imaginable. Apart from their use in fill level sensors, the floating body gravimeter according to the invention and the above described gravitational field analysis methods according to the invention can also advantageously be used in other applications of qualitative and quantitative detection of masses or of their volumes. With only a single type of gravimeter circuit all types of measuring applications can be covered because the earth's gravitational field represents the dominant variable in all these cases. Furthermore, apart from the acquisition of gravitational acceleration, the floating-body measuring cell according to the invention can also be used to measure other types of - 58 acceleration. When compared to known acceleration sensors, said floating-body measuring cell according to the invention provides advantages in particular when measuring very small acceleration values and can thus, for example, be used in inertial navigation systems for vehicles, including submarines and aerodynamic vehicles. In addition, it should be pointed out that "comprising" does not exclude other elements or steps, and "a" or "one" does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above exemplary embodiments can also be used in combination with other characteristics or steps of other exemplary embodiments described above. Reference characters in the claims are not to be interpreted as limitations.

Claims

1. A gravimeter unit for determining a gravitational field intensity, the gravimeter unit comprising: 5 a source for generating a field, the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; a first floating body that can be kept afloat in a contactless manner by a field generated by the source; a first detector, a first position of the first floating body can be detected by the to first detector, the first detector comprising a second electrode for detecting the first position of the first floating body; wherein the gravimeter unit is adapted to determine first data on the basis of the detected first position or of the generated field, the first data corresponding to a first gravitational field intensity in a first location, the gravimeter unit being provided on a 15 semiconductor chip.

2. The gravimeter unit according to claim 1, wherein the first detector is adapted for capacitive, inductive, conductive or optical detection of the first position of the first floating body.

3. The gravimeter unit according to claim 1 or 2, further comprising: 20 a second floating body; and a second detector, a second position of the second floating body can be detected by the second detector; and wherein the gravimeter unit is adapted to generate the first data on the basis of the measured first position and of the measured second position. 25 4. The gravimeter unit according to any one of claims 1 to 3, further comprising: a control device; wherein the control device is adapted to hold the first floating body in its home position. 30 5. A sensor for material detection by means of gravitational field analysis, with the sensor comprising: a first gravimeter unit according to any one of claims I to 4 adapted to determine first data that corresponds to a first gravitational field intensity at a first location; 812369 (3212956 1) -60 a second gravimeter unit according to any one of claims I to 4 adapted to determine second data that corresponds to a second gravitational field intensity at a second location; and a communication interface adapted to transmit the first data and the second data 5 to an analysis unit.

6. The sensor according to claim 5, wherein: the determined first data is based on first floating-body position data or on first closed-loop control parameters of a first closed-loop control device; and the determined second data is based on second floating-body position data or on 1o second closed-loop control parameters of a second closed-loop control device.

7. A method for fill level measuring a product in a tank by means of gravitational field analysis, with the method comprising the following steps: generating a field by a source, the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; 15 detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field generated by the source, the first detector comprising a second electrode for detecting the first position of the first floating body; determining first data corresponding to a first gravitational field intensity at a 20 first location, by the first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; determining second data corresponding to a second gravitational field intensity at a second location, by a second gravimeter unit; calculating a fill level of the product, on the basis of the determined first and 25 second data.

8. The use of a sensor according to claim 5 or 6 as a fill-level measuring device or a proximity sensor.

9. The use of a gravimeter unit according to any one of claims 1 to 4 as a fill level sensor or a proximity sensor. 30 10. The use of a gravimeter unit according to any one of claims 1 to 4 as an acceleration meter. 812369(3212956 1) -61 1. A program element for measuring the fill level of a product in a tank by means of gravitational field analysis, wherein the program element when it is executed on a processor instructs the processor to carry out the following operations: generating a field by a source, the field being an electrical field, the source 5 comprising at least a first electrode for generating the electrical field; detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field generated by the source, the first detector comprising a second electrode for detecting the first position of the first floating body; 1o determining first data corresponding to a first gravitational field intensity at a first location, by a first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; determining second data corresponding to a second gravitational field intensity at a second location, by a second gravimeter unit; is calculating a fill level of the product on the basis of the determined first and second data.

12. A computer-readable storage medium on which a computer program for measuring the fill level of a product in a tank by means of gravitational field analysis is stored, wherein the computer program when it is executed on a processor instructs the 20 processor to carry out the following operations: generating a field by a source, the field being an electrical field, the source comprising at least a first electrode for generating the electrical field; detecting a first position of a first floating body of a first gravimeter unit by a first detector, the first floating body being kept afloat in a contactless manner by a field 25 generated by the source, the first detector comprising a second electrode for detecting the first position of the first floating body; determining first data corresponding to a first gravitational field intensity at a first location, by a first gravimeter unit, the first data being determined on the basis of the detected first position or of the generated field; 30 determining second data corresponding to a second gravitational field intensity at a second location, by a second gravimeter unit; calculating a fill level of the product on the basis of the determined first and second data. 812369(3212956 1) -62

13. A gravimeter unit substantially as hereinbefore described with reference to any one of the embodiments as that embodiment is shown in one or more of the accompanying drawings.

14. A sensor for material detection by means of gravitational field analysis, 5 the sensor substantially as hereinbefore described with reference to the accompanying drawings.

15. A method for fill level measuring a product in a tank by means of gravitational field analysis, the method substantially as hereinbefore described with reference to the accompanying drawings. to 16. The use of a sensor for material detection by means of gravitational field analysis, the use substantially as hereinbefore described with reference to the accompanying drawings.

17. The use of a gravimeter unit, the use substantially as hereinbefore described with reference to the accompanying drawings. is 18. A program element for measuring the fill level of a product in a tank by means of gravitational field analysis, wherein the program element when it is executed on a processor instructs the processor to carry out the operations substantially as hereinbefore described with reference to any one of the embodiments as that embodiment is shown in one or more of the accompanying drawings. 20 18. A computer-readable storage medium on which a computer program for measuring the fill level of a product in a tank by means of gravitational field analysis is stored, wherein the computer program when it is executed on a processor instructs the processor to carry out the operations substantially as hereinbefore described with reference to any one of the embodiments as that embodiment is shown in one or more of 25 the accompanying drawings. Dated 18th Day of February 2011 Vega Grieshaber KG Patent Attorneys for the Applicant/Nominated Person 30 SPRUSON & FERGUSON 812369(3212956_1)