Capacitive oil sensor, oil sensor set and procedure for calibrating a capacitive oil sensor

Abstract

Capacitive oil sensor (1) comprising a first electrode (2) and a second electrode (3), wherein an outwardly open first receiving chamber (4) for oil to be examined is formed between the first electrode (2) and the second electrode (3), wherein the first electrode (2) and the second electrode (3) form a first capacitor (5), wherein a third electrode (6) is formed, wherein the third electrode (6) is electrically connected to the first electrode (2), wherein the second electrode (3) is arranged between the first electrode (2) and the third electrode (6), wherein an outwardly open second receiving chamber (7) for oil to be examined is formed between the second electrode (3) and the third electrode (6), and wherein the second electrode (3) and the third electrode (6) form a second capacitor (8), characterized in that the first electrode (2) and the third electrode (6) project laterally beyond the second electrode (3).that the first electrode (2) and the third electrode (6) are connected and / or configured as neutral electrodes and that a temperature sensor is arranged in the first, neutral electrode (2) and / or in the third, neutral electrode (6).

Description

[0001] The invention relates to a capacitive oil sensor having a first electrode and a second electrode, wherein a first receiving space for oil to be examined, which is open to the outside, is formed between the first electrode and the second electrode, and wherein the first electrode and the second electrode form a first capacitor.

[0002] Such arrangements are known, for example, for assessing the quality of frying oil or other oils. An electronic circuit is connected to the first electrode and the second electrode, with which the capacitance of the first capacitor can be measured. A measuring frequency is often applied, and the electronic circuit is an oscillator circuit. Since the resonant frequency of this oscillator circuit is co-determined by the capacitance of the capacitor, a conclusion can be drawn about the dielectric constant in the first receiving chamber. The dielectric constant, in turn, provides information about the composition and condition of the oil being examined, which allows the quality of the oil to be assessed.

[0003] With the known arrangements, it is important to ensure that no additional objects interfere with the capacitor's stray field during the measurement process and thus falsify the measurement result. Such additional objects can be, for example, the wall of a frying oil pan or a frying basket, or other, particularly metallic, objects or instruments used in the frying oil. If such an object is located in the capacitor's stray field, the influence of this object on the aforementioned resonant frequency is often so great that the change in the frying oil due to degradation or the like is no longer measurable.

[0004] The invention further relates to an oil sensor set with a capacitive oil sensor, wherein at least one first capacitor with an outwardly open, first receiving space for oil to be examined is formed on the oil sensor, and with a calibration means for calibrating the oil sensor.

[0005] Oil sensor sets are well known and are delivered with, for example, the oil sensors described above. Due to changes in the oil sensors over time, they must be calibrated regularly.

[0006] Finally, the invention relates to a method for calibrating a capacitive oil sensor.

[0007] The invention is based on the object of creating an easy-to-handle capacitive oil sensor.

[0008] DE 101 55 371 A1 discloses a sensor for determining the dielectric constant of a fuel. This sensor serves to distinguish between different fuel types by determining their different dielectric constants. For this purpose, this sensor has a capacitor arrangement with concentric capacitor electrodes.

[0009] DE 198 06 477 C1 relates to a method and a measuring device for determining the volumetric gas content in a two-phase flow of a medium comprising a gas phase and a liquid phase with an unknown flow pattern.

[0010] From DE 11 2006 002 385 T5 a sealed capacitive rain sensor is known which, in the position of use, is attached to a windshield of a vehicle.

[0011] From EP 2 163 887 A1, a method for measuring physical quantities of electrically low-conductive and non-conductive fluids is already known, wherein the fluid is located between electrically conductive electrodes of a base sensor, wherein a test signal in the form of a clocked DC voltage or a clocked DC current is applied to the base sensor, the resulting output current or the output voltage is integrated by means of an integrator, the output signal of which is applied, optionally via an amplifier, to a first Schmitt trigger, the output signal of which is in turn applied as a test signal to the base sensor, wherein the output signal is also applied to a second Schmitt trigger, which is connected in parallel to the first Schmitt trigger and serves as a comparator, wherein the output signal of both Schmitt triggers is applied to an XOR gate,from whose output signals the physical quantities of the fluid to be measured are calculated via a microcomputer and fed to an evaluation logic, whereby both the resistance and the capacitance are determined from the measured signal.

[0012] US 4,854,725 A discloses a measuring arrangement for monitoring steam flowing through a pipeline. This measuring arrangement comprises three electrodes, each of which is connected to the neutral electrode formed by the housing of this measuring arrangement.

[0013] From US 5 418 465 A, a cell for measuring a mixing ratio of a liquid is previously known, comprising: a first elongate member; a second elongate member coupled opposite and adjacent to the first elongate member, the first and second elongate members defining a passage therebetween, the passage having an inlet for receiving the liquid and an outlet for discharging the liquid; a first electrode coupled to the first elongate member adjacent to the passage; a second electrode coupled to the second elongate member adjacent to the passage;and at least one interconnect layer disposed between the first elongate member and the second elongate member to couple the first and second elongate members, the interconnect layer and the first and second elongate members defining the passageway, the interconnect layer being made of glass and patterned using a thick film technique, at least one of the first and second electrodes being deposited onto a corresponding one of the first and second elongate members using the thick film technique;

[0014] From US 4,555,661 A, a method for measuring the dielectric constant of a material in a container is previously known, comprising the following steps: arranging an electrode device in the container, the electrode device having a first, a second, and a third electrode that are spatially spaced from one another, the third electrode being arranged between the first and the second electrode; connecting the first and the second electrode via a first and a second terminal to a first and a second electrical potential, respectively, and leaving the third electrode at a floating electrical potential;Measuring a first value of an electrical signal across the first and second electrodes that is proportional to the product of the dielectric constant of the material and the distance between the first and second electrodes while keeping the area and end effects of the electrodes substantially constant; electrically switching the third electrode from the floating electrical potential to an electrical potential equal to the first electrical potential; measuring a second value of an electrical signal across the second and third electrodes that is proportional to the product of the dielectric constant of the material and the distance between the second and third electrodes while keeping the area and end effects of the electrodes substantially constant; calculating a third value equal to the difference between the first and second values;and calculating the dielectric constant of the material based on the third value.;

[0015] From US 6 617 968 ​​B1, a drive axle housing of a motor vehicle is previously known, the axle housing comprising: an enlarged central portion accommodating a differential assembly; the central portion forming an oil reservoir containing a predetermined amount of lubricating oil; a pair of opposing axle tubes extending from the central portion;and a capacitive oil level sensor mounted on the central portion of the drive axle housing and provided for measuring an oil level in the oil reservoir, wherein the oil level sensor is partially immersed in the oil reservoir, and wherein the capacitive oil level sensor comprises: an L-shaped housing having a first leg at least partially immersed in the oil reservoir and a second leg arranged substantially perpendicular to the first leg and extending substantially horizontally out of the drive axle housing, wherein the first leg accommodates an oil level sensing capacitor at least partially immersed in the oil reservoir for sensing the oil level;

[0016] From US 5 614 830 A a method for assessing the presence of contaminants suspended in a lubricating oil sample is previously known, the method comprising the following steps: carrying a stagnant quantity of sample oil through a capacitively responsive surface in direct interface therewith to receive deposits of gravity-influenced fluids and particles suspended in the sample; applying a magnetic field to the oil sample oriented to induce movement of magnetically responsive particles suspended in the sample towards the responsive surface; measuring and reporting the capacitive response of the surface to gravity and the magnetically induced deposition of suspended particles thereon for a measured period of time.

[0017] A measuring cell for measuring the electrical conductivity of flowing liquids contaminated by electrically conductive impurities is previously known from DE 1 180 551 A. This measuring cell is characterized by the fact that the electrode arrangement consists of a plurality of disc-shaped, coaxially arranged electrodes, which are alternately connected to one pole of a potential difference and to the other pole of a potential difference.

[0018] To achieve this object, the features of claim 1 are provided according to the invention. In particular, in a capacitive oil sensor of the type described at the outset, it is proposed according to the invention that a third electrode is formed, that the third electrode is electrically connected to the first electrode, that the second electrode is arranged between the first electrode and the third electrode, that a second receiving space, open to the outside, for oil to be examined is formed between the second electrode and the third electrode, and that the second electrode and the third electrode form a second capacitor.The inventive arrangement of the second electrode between the first electrode and a third electrode provides shielding, or at least partial shielding, of the second electrode, so that the influence of metallic objects in the immediate vicinity of the capacitive oil sensor on the capacitance measurement result can be reduced. This simplifies the handling of the capacitive oil sensor, as careful maintenance of a minimum distance from metallic objects during measurement is no longer necessary.

[0019] According to the invention, the first electrode and the third electrode are designed and / or wired as a neutral electrode. This advantageously allows the second electrode to be shielded from the outside. This further reduces the influence of stray fields on the capacitance measurement. In this case, the second electrode can be designed and / or wired as a live electrode.

[0020] In one embodiment of the invention, an electronic circuit can be connected to the first electrode and the second electrode, with which the total capacitance of the first capacitor and the second capacitor can be determined. Advantageously, the known method for determining the quality of an oil to be tested can be implemented based on measuring the dielectric constant of the oil.

[0021] Thus, the aforementioned first electronic circuit, which can be used to determine the capacitance of the second capacitor, can be connected to the second electrode and the third electrode. Advantageously, the first and second receiving chambers can be used together to measure the dielectric constant. Thus, the sum of the two capacitances can be determined.

[0022] In one embodiment of the invention, it can be provided that the first electrode is disk-shaped. Alternatively or additionally, it can be provided that the second electrode is disk-shaped. Alternatively or additionally, it can be provided that the third electrode is disk-shaped. The aforementioned electrodes can be designed individually or jointly as circular disks, which is particularly advantageous for production. Alternatively, the electrodes can also be designed with other contours, for example triangular, square, pentagonal, hexagonal, octagonal, elliptical or free-form contours. The disk-shaped design of the electrodes has the advantage that the oil sensor can be easily assembled by assembling the disk-shaped electrodes, for example in a stacked arrangement.

[0023] In one embodiment of the invention, it can be provided that the first and / or second receiving chamber is / are annular. This is advantageous because it allows for the oil to be analyzed to be received from all sides. It is also advantageous that the respective receiving chamber is easily accessible and / or easy to clean.

[0024] In one embodiment of the invention, it can be provided that a dimension of the first and / or second receiving space along a direction of extension of the first or second electrode is larger than a dimension of the first or second receiving space transverse to the direction of extension. This advantageously creates an elongated, for example, annularly closed or rectilinear receiving space that is easy to clean. It is particularly advantageous if the dimension of the respective receiving space along the direction of extension is at least twice or even at least ten times the dimension of the respective receiving space transverse to the direction of extension. This makes it possible to form slot- and / or groove-shaped receiving spaces.

[0025] In one embodiment of the invention, the first receiving chamber and the second receiving chamber can be of equal size. This is advantageous because the same volume of oil to be tested can be filled into both receiving chambers, making the measurement results comparable. It is particularly advantageous if the first receiving chamber and the second receiving chamber are congruent with each other. This is advantageous because identical geometric proportions are realized, so that capacitive measurements in the receiving chambers are comparable.

[0026] In one embodiment of the invention, the first, second, and third electrodes can be aligned coaxially and / or centered relative to one another. This advantageously allows for the formation of a rod-shaped arrangement that is easy to handle.

[0027] Alternatively or additionally, at least one mandrel may be formed on the third electrode, onto which the first electrode and / or the second electrode is / are mounted. This is advantageous in that automatic centering and / or coaxial alignment of the electrodes relative to one another can be achieved easily. A further advantage is that the oil sensor can be easily mounted by simply mounting the electrodes on top of one another.

[0028] In one embodiment of the invention, it can be provided that the first, second, and / or third electrode is / are mechanically dimensionally stable. This is advantageous because deformation of the electrodes due to improper use can be largely ruled out. This ensures that the measuring properties of the oil sensor are maintained over a long period of time, even under harsh operating conditions. For example, the first, second, and / or third electrode can each be formed as a turned part or together as a turned part. This makes it possible to manufacture the capacitive oil sensor using a turning process.

[0029] In one embodiment of the invention, it can be provided that an insulating body is arranged between the first electrode and the second electrode. Alternatively or additionally, it can be provided that an insulating body is arranged between the second electrode and the third electrode. This is advantageous in that the insulating body can serve as a spacer between the electrodes, thus preventing a change in the size of the respective receiving space. It is particularly advantageous if the respective insulating body is made of ceramic. This enables simple production of the insulating body or bodies with good insulation properties. A separate insulating body can be arranged between each pair of electrodes, or a common insulating body can be formed, extending both between the first electrode and the second electrode and between the second electrode and the third electrode.

[0030] In this case, the insulating body arranged between the electrodes can be provided with a metallic coating. It is advantageous in this case that the metallic coating can be subjected to a voltage whose profile is synchronized with the voltage profile between the first electrode and the second electrode, or between the second electrode and the third electrode. In this way, any influence of the respective insulating body on the measurement of the dielectric constant in the receiving space can be compensated.

[0031] In this case, an insulating layer can be arranged between a metallic coating, for example, the aforementioned metallic coating of the insulating body, and the respective electrodes. This is advantageous because it allows for galvanic isolation between the metallic coating of the insulating body and the electrodes.

[0032] According to the invention, the first electrode and / or the third electrode project laterally beyond the second electrode. Advantageously, the second electrode can be shielded from the outside by the first electrode and / or the third electrode. This prevents, for example, external metallic objects from altering the stray field of the first capacitor or the second capacitor in such a way that the capacitance measurement result is significantly altered.

[0033] In this case, the first electrode and / or the third electrode can project beyond the second electrode transversely to a connecting line between the first electrode and the third electrode. This allows the second electrode to be completely enclosed within a space defined by the first electrode and the third electrode. This ensures that the stray field components during capacitance measurement are kept very low. Sources of measurement error can thus be reduced or even completely avoided.

[0034] According to the invention, a temperature sensor is arranged in the first electrode. It is also provided that the temperature sensor is arranged in the second electrode and / or the third electrode. A temperature sensor makes it possible to detect and computationally compensate for temperature effects related to the expansion of the material and the dielectric constant of the oil being tested. According to the invention, the temperature sensor is arranged in the neutral electrode. In this way, additional parasitic capacitances can be avoided.

[0035] To achieve the stated object, the invention provides for an oil sensor set of the type described above that the calibration means has a first test specimen of known dielectric constant, wherein the first test specimen can be inserted into the first receiving space for capacitance measurement. Advantageously, the capacitance measurement can be carried out with a known dielectric constant in at least part of the receiving space. Thus, parameters used to calculate the dielectric constant of the oil to be tested can be determined. The inventive use of a solid test specimen has the further advantage that no liquids need to be handled for calibration.

[0036] In one embodiment of the invention, the first test specimen can completely fill the receiving space. This is advantageous because the influence of air does not need to be taken into account during calibration. Alternatively, the first test specimen can partially fill the receiving space. This is advantageous because the test specimen is easy to insert.

[0037] In one embodiment of the invention, it can be provided that a second test specimen can be inserted into the first receiving space, wherein the second test specimen has a volume that differs from the first test specimen. The calibration device thus has at least two test specimens. This is advantageous in that different volume fractions of the receiving space with a known dielectric constant can be filled with the test specimens. This allows two measuring points to be obtained as reference points for calibration. Alternatively or additionally, it can be provided that the second test specimen has a dielectric constant that differs from the first test specimen. This is advantageous in that the calibration measurement can be carried out with different dielectric constants.

[0038] The use of a test specimen that only partially fills the first receiving space and / or the second receiving space has the advantage that an oil sensor with an annular receiving space can be calibrated with the test specimen without the test specimen having to be destroyed for assembly or the oil sensor having to be dismantled.

[0039] To achieve the stated object, the invention provides for a method of the type mentioned at the outset that a first test specimen with a known dielectric constant is inserted into a receiving space for oil, for example the already mentioned first receiving space or second receiving space of a capacitive oil sensor according to the invention, of at least one capacitor, and that a capacitance of the at least one capacitor is measured with the first test specimen inserted. It is advantageous that the standard measuring method of the capacitive oil sensor can be used directly for calibration. A further advantage is that solid test specimens can be used, so that subsequent cleaning and / or drying of the oil sensor after calibration is unnecessary.

[0040] Alternatively, the first test specimen can be made of an electrically conductive material. Such a test specimen reduces the volume of the receiving space, thus changing the properties of the capacitor and thus its capacitance. If this volume of the test specimen is known, the test specimen can also be used to calibrate the capacitive oil sensor. The first test specimen can be designed to electrically contact an electrode.

[0041] In one embodiment of the invention, the capacitance of the at least one capacitor can be measured without a first test specimen and / or with a second test specimen with a known dielectric constant or made of an electrically conductive material. Advantageously, two measurement points can be provided for calibration. If the volumes of the first and second test specimens differ, different capacitors with different capacitances result, allowing a second calibration.

[0042] In one embodiment of the invention, it can be provided that the second test specimen occupies a smaller volume portion of the receiving space than the first test specimen and / or that the dielectric constant of the second test specimen differs from the dielectric constant of the first test specimen. This is advantageous in that two defined measurement conditions for calibration can be easily established.

[0043] It is particularly advantageous if an oil sensor according to the invention, in particular as described above and / or according to one of the claims directed to an oil sensor, is used in the method according to the invention. For example, an oil sensor according to the invention from an oil sensor set according to the invention can be used for this purpose.

[0044] The invention will now be described in more detail with reference to exemplary embodiments, but is not limited to these exemplary embodiments. Further exemplary embodiments arise from combining the features of individual or multiple claims with one another and / or with individual or multiple features of the exemplary embodiments.

[0045] It shows: Fig. 1 a capacitive oil sensor according to the invention in a three-dimensional oblique view, Fig. 2 the capacitive oil sensor according to the invention Fig. 1 in an axial section and a test specimen to explain the method according to the invention, Fig. 3 shows another capacitive oil sensor according to the invention, Fig. 4 an electronic circuit to explain the oil sensor according to Fig. 1 or an oil sensor according to Fig. 3 executable capacity measurement and Fig. 5 shows a further capacitive oil sensor according to the invention in a view along a direction of extension of the electrodes and above in a view from the side.

[0046] Fig. 1 shows a capacitive oil sensor, designated as a whole by 1, in a three-dimensional oblique view, wherein details not required for the description of the invention are omitted to simplify the illustration.

[0047] The oil sensor 1 has a first electrode 2 and a second electrode 3, which enclose a first receiving space 4 between them.

[0048] The first receiving chamber 4 is open to the outside in order to receive oil to be examined.

[0049] The first electrode 2 and the second electrode 3 thus form a first capacitor 5, the capacitance of which is determined by a medium located in the first receiving space 4.

[0050] The oil sensor 1 has a third electrode 6, which, together with the second electrode 3, defines a second receiving chamber 7. The second receiving chamber 7 is open to the outside to accommodate oil to be analyzed.

[0051] The second electrode 3 and the third electrode 6 form a second capacitor 8, the capacitance of which is determined by a medium located in the second receiving space 7.

[0052] The first electrode 2 and the third electrode 6 are electrically connected to each other so that the first electrode 2 and the third electrode 6 are at the same potential.

[0053] The second electrode 3 is arranged between the first electrode 2 and the third electrode 6, so that the second electrode 3 is at least partially electrically shielded from the outside.

[0054] Fig. Figure 4 shows an electronic circuit with which the capacitive oil sensor 1 can be connected. A highly simplified circuit is shown, which is intended to explain the principle of the invention. Details known to those skilled in the art but not absolutely necessary for explaining the invention have been omitted for the sake of simplicity.

[0055] In Fig. 4 it can be seen that the first electrode 2 is electrically connected to the second electrode 6.

[0056] An electronic circuit 9 is connected to the first electrode 2 and the third electrode 6 on the one hand and to the second electrode 3 on the other hand in order to measure the capacitance of the first capacitor 5 and the second capacitor 8.

[0057] For this purpose, an alternating voltage signal is applied in a conventional manner.

[0058] Fig. 2 shows an axial section of the capacitive oil sensor 1 according to Fig. 1.

[0059] It can be seen that the first electrode 2 and the third electrode 6 are electrically connected to each other, while the first electrode 2 and the third electrode 6 are galvanically separated from the second electrode 3.

[0060] In Fig. 1 shows that the electrodes 2, 3, and 6 are each disk-shaped. Each of the electrodes 2, 3, and 6 is formed as a circular disk.

[0061] This means that the first receiving space 4 and the second receiving space 7 are each ring-shaped.

[0062] The receiving spaces 4, 7 are groove-shaped, wherein a dimension of the respective receiving space 4, 7 along a - here also annular - direction 10 is larger than a dimension of the respective receiving space 4, 7 transverse to this direction 10.

[0063] It is also evident that the first receiving space 4 and the second receiving space 7 are formed congruently with each other, so that the receiving spaces 4, 7 are formed of the same size as each other.

[0064] In Fig. 2 it can be seen that a rod-shaped mandrel 11 is formed on the third electrode 6.

[0065] The first electrode 2 and the second electrode 3 are placed on this mandrel 11 and have corresponding central bores 12.

[0066] This makes it easy to achieve a coaxial and centered alignment of the electrodes 2, 3, 6.

[0067] The electrodes 2, 3, 6 are designed as turned parts and have mechanical dimensional stability.

[0068] The metallic mandrel 11 establishes the electrical connection between the first electrode 2 and the third electrode 6.

[0069] An insulating body 13 is formed between each of the electrodes 2, 3, and 6. The insulating bodies 13 are also disc-shaped, each with a central bore, and are placed on the mandrel 11.

[0070] The electrode 2 can be screwed onto the mandrel 11 to prevent the electrodes 2, 3, 6 and / or insulating body 13 from falling apart.

[0071] The dimensional stability of the electrodes 2, 3, 6 is sufficient to apply and dissipate the required holding forces.

[0072] The insulating bodies 13 are made of ceramic.

[0073] In Fig. 2, it is particularly clearly visible that the outer electrodes 2, 6 project laterally beyond the inner electrode 3, so that the radial dimension of the capacitive oil sensor 11 is determined by the first electrode 2 and the third electrode 6. In the exemplary embodiment, the electrodes 2, 6 thus project radially beyond the electrode 3 and transversely to a connecting line between the first electrode 2 and the third electrode 6.

[0074] In other words, the second electrode 3 is arranged in the shadow behind the respective adjacent electrode 2, 6, so that a stray field of the first capacitor 5 or the second capacitor 8 runs essentially within a volume predetermined by the outer electrodes 2, 6.

[0075] In this way, external objects can only have a minimal influence on the capacitance measurements.

[0076] Fig. Figure 3 shows a further capacitive oil sensor 1 according to the invention in a highly simplified schematic diagram. Components and functional units that are functionally and / or structurally similar or identical are designated by the same reference numerals and are not described separately. Fig. 1, Fig. 2 and Fig. 4 therefore apply to Fig. 3 accordingly.

[0077] The embodiment according to Fig. 3 differs from the embodiment according to Fig. 1 and Fig. 2 in that the direction of travel 10 is not closed in a ring shape, but extends linearly. This results in the Fig. 3 shows a stacked arrangement of the electrodes 2, 3, 6 on top of each other. The insulating bodies 13 are in the embodiment according to Fig. 3 are provided with a coating 14 or 15, which in the circuit according to Fig. 4. The coatings 14, 15 are each designed as metallic coatings.

[0078] In order to achieve potential separation, insulating layers 16 are inserted between the coatings 14, 15 and the electrodes 2, 3, 6.

[0079] This means that the Fig. 4 shown capacitors 17.

[0080] About the Fig. In the circuitry of an operational amplifier 18 shown in Figure 4, a voltage on the coatings 14, 15 is carried along with the voltage curve on the second electrode 3, so that an influence of the insulating bodies 13 on the capacitance measurements of the capacitors 5, 8 is compensated.

[0081] Fig. Figure 5 shows a further capacitive oil sensor according to the invention. Components and functional units that are structurally and / or functionally similar or identical to the preceding embodiments are designated by the same reference numerals and will not be described separately again. Fig. 1 to 4 therefore apply to Fig. 5 accordingly.

[0082] The embodiment according to Fig. 5 differs from the preceding embodiments in that the first electrode 2 and the third electrode 6 are integrally connected to one another and made from a single piece. The first electrode 2 and the third electrode 6 can be made from a solid or hollow cylinder, in which the receiving spaces 4 and 7 are formed by material removal or cutting.

[0083] The second electrode is arranged between the first electrode 2 and the third electrode 6, with the first electrode 2 and the third electrode 6 projecting laterally beyond the second electrode 3 transversely to the connecting line between the first electrode 2 and the third electrode 6. Thus, the second electrode 3 is arranged and accommodated entirely within a space 23, which is delimited from the outside by the first electrode 2 and the third electrode 6.

[0084] The capacitive oil sensor 1 thus consists of a solid metal cylinder into which a space 23 in the form of a slot is milled and at one end of which a bore 24 is formed.

[0085] The second electrode 3 is inserted through the bore 24, which bore is filled with an insulating body 13.

[0086] The second electrode 3 is connected to an electronic circuit 9 (not shown here) via a connecting line 25. The second electrode 3 is thus designed as a voltage-carrying electrode.

[0087] The first electrode 2 and the third electrode 6 are connected to a metallic sensor tube 26, which also serves as a mass supply.

[0088] The first electrode 2 and the third electrode 6 are therefore designed as neutral electrodes.

[0089] In the embodiments shown, in particular in the embodiments according to Fig. 1 and Fig. 2 or Fig. 3, the arrangement of the capacitors 5, 8 can also be extended to a stack arrangement with a plurality of alternately contacted electrodes 2, 3, 6.

[0090] It should also be noted that in the illustrated embodiments and in further embodiments, the temperature sensor 21 is arranged in a cavity 27 of the respective electrode 2, 3, or 6, wherein this cavity 27 is at least partially filled with thermal paste 22. Temperature influences on the capacitance measurement can be compensated for and are compensated for using an output signal from the temperature sensor 21.

[0091] To calibrate the oil sensor 1 according to Fig. 1 - and analogously according to Fig. 3 - an oil sensor set 19 is provided, which Fig. 2 shows.

[0092] The oil sensor set 19 has the already described oil sensor 1 and at least one solid test body 20, which can be inserted into the first receiving space 4 and / or into the second receiving space 7 and completely or partially fills the respective receiving space 4, 7.

[0093] In the embodiment according to Fig. 1 and Fig. 2, the test specimen 20 can be formed in the shape of a ring segment, in the embodiment according to Fig. 3, the test specimen 20 can be flat and even.

[0094] The dielectric constant of specimen 20 is known.

[0095] If the test specimen 20 is arranged in one of the receiving spaces 4, 7 or in both receiving spaces 4, 7, the capacitance measurement can be carried out with a known dielectric constant in the receiving space 4, 7. This means that parameters with which the dielectric constant of the medium in the receiving space 4, 7 can be determined can be specified or adjusted.

[0096] The oil sensor set 19 can comprise additional test specimens similar to the test specimen 20, which can have a different shape or size to fill the receiving chamber 4, 7 in different ways. Alternatively or additionally, the additional test specimens 20 can have a different dielectric constant to provide different measurement conditions. This can be achieved, for example, by selecting different materials.

[0097] If the capacitance is measured during calibration with and without the test specimen 20 inserted, the medium air with a known dielectric constant is available as the second measurement condition. If another test specimen is used instead of the test specimen 20, the second measurement conditions are determined by its – possibly different – ​​dielectric constant and its – possibly different – ​​filling of the receiving space 4, 7.

[0098] It should also be mentioned that the electrical connection between the first electrode 2 and the third electrode 6 largely compensates for a temperature dependence that arises in the oil sensor 1 due to thermal expansion. This is because the inventive arrangement of the second electrode 3 between the interconnected electrodes 2 and 6 ensures that the sum of the capacitances of the first capacitor 5 and the second capacitor 8 is measured. Although thermal expansion may change the ratio of the capacitances to one another, the sum of the capacitances remains largely constant, thus achieving temperature stability.

[0099] In the capacitive oil sensor 1 with a first electrode 2 and a second electrode 3, which enclose an outwardly open receiving space 4 between them to form a first capacitor 5, it is proposed to arrange the second electrode 3 between the first electrode 2 and a third electrode 6, wherein the first electrode 2 is electrically connected to the third electrode 6 and wherein the second electrode 3 and the third electrode 6 define a second receiving space 7 and form a second capacitor 8.

Claims

[1] Capacitive oil sensor (1), with a first electrode (2) and a second electrode (3), wherein an outwardly open, first receiving space (4) for oil to be analyzed is formed between the first electrode (2) and the second electrode (3), wherein the first electrode (2) and the second electrode (3) form a first capacitor (5), wherein a third electrode (6) is formed, wherein the third electrode (6) is electrically connected to the first electrode (2), wherein the second electrode (3) is arranged between the first electrode (2) and the third electrode (6), wherein an outwardly open, second receiving space (7) for oil to be analyzed is formed between the second electrode (3) and the third electrode (6), and wherein the second electrode (3) and the third electrode (6) form a second capacitor (8), characterized bythat the first electrode (2) and the third electrode (6) project laterally beyond the second electrode (3), that the first electrode (2) and the third electrode (6) are wired and / or designed as neutral electrodes and that a temperature sensor is arranged in the first, neutral electrode (2) and / or in the third, neutral electrode (6). [2] Capacitive oil sensor (1) according to claim 1, characterized by that an electronic circuit (9) is connected to the first electrode (2) and the second electrode (3), with which a total capacitance of the first capacitor (5) and the second capacitor (8) can be determined. [3] Capacitive oil sensor (1) according to claim 1 or 2, characterized by that the first electrode (2) and / or the second electrode (3) and / or the third electrode (6) is / are disc-shaped, in particular as circular discs, and / or that the first (4) and / or the second receiving space (7) is / are annular. [4] Capacitive oil sensor (1) according to one of claims 1 to 3, characterized by that the first electrode (2) and / or the second electrode (3) and / or the third electrode (6) is / are designed as circular discs. [5] Capacitive oil sensor (1) according to one of claims 1 to 4, characterized by that a dimension of the first (4) and / or second receiving space (7) along a direction of extension (10) of the first (2) and / or second electrode (3) is greater than a dimension of the first (4) and / or second receiving space (7) transverse to the direction of extension (10) and / or that the first receiving space (4) and the second receiving space (7) are of the same size and / or congruent with one another. [6] Capacitive oil sensor (1) according to one of claims 1 to 5, characterized bythat the first (2), second (3) and third electrode (6) are aligned coaxially and / or centered with respect to one another and / or that at least one mandrel (11) is formed on the third electrode (6), onto which mandrel the first electrode (2) and / or the second electrode (3) is / are placed. [7] Capacitive oil sensor (1) according to one of claims 1 to 6, characterized by that the first (2), second (3) and / or third electrode (6) is / are designed to be mechanically dimensionally stable, in particular as a turned part(s). [8] Capacitive oil sensor (1) according to one of claims 1 to 7, characterized by that the first (2), second (3) and / or third electrode (6) is / are designed as a turned part(s). [9] Capacitive oil sensor (1) according to one of claims 1 to 8, characterized by that an insulating body (13), in particular made of ceramic, is arranged between the first electrode (2) and the second electrode (3) and / or between the second electrode (3) and the third electrode (6). [10] Capacitive oil sensor (1) according to claim 9, characterized by that the insulating body (13) arranged between the electrodes (2, 3, 6) is provided with a metallic coating (14, 15) and / or that an insulating layer (16) is arranged between the or a metallic coating (14, 15) of the insulating body (13) and the electrodes (2, 3, 6). [11] Capacitive oil sensor (1) according to one of claims 1 to 10, characterized by that the first electrode (2) and / or the third electrode (6) project laterally beyond the second electrode (3) transversely to a connecting line between the first electrode (2) and the third electrode (6) and / or that a temperature sensor is arranged in the second electrode (3). [12] Oil sensor set (19) with a capacitive oil sensor (1) according to one of claims 1 to 11, wherein at least one first capacitor (5) with an outwardly open, first receiving space (4) for oil to be examined is formed on the oil sensor (1), and with a calibration means for calibrating the oil sensor (1), wherein the calibration means has a first test body (20) of known dielectric constant, wherein the first test body (20) can be inserted into the first receiving space (4) for capacitance measurement. [13] Oil sensor set (19) according to claim 12, characterized by that the first test body (20) completely or partially fills the receiving space (4) and / or that a second test body can be inserted into the first receiving space (4), wherein the second test body has a volume different from that of the first test body (20) and / or a dielectric constant different from that of the first test body (20). [14] Method for calibrating a capacitive oil sensor (1) according to one of claims 1 to 11, wherein a first test body (20) with a known dielectric constant or made of an electrically conductive material is inserted into a receiving space (4, 7) for oil of at least one capacitor (5, 8), and that a capacitance of the at least one capacitor (5, 8) is measured with the first test body (20) inserted. [15] Method according to claim 14, characterized by that the capacitance of the at least one capacitor (5, 8) is measured without a first test body (20) inserted and / or with a second test body inserted with a known dielectric constant or made of an electrically conductive material. [16] Method according to claim 15, characterized bythat the second test specimen occupies a smaller volume fraction of the receiving space than the first test specimen (20) and / or that the dielectric constant of the second test specimen is different from the dielectric constant of the first test specimen (20).

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