Sensor device for detecting the dielectric strength of a dielectric fluid, in particular a fluid for temperature regulation of batteries - Patents.com

Abstract

The sensor device for detecting the dielectric strength of a dielectric fluid has a sensor body supporting a sensitive part (SG1) designed to be in contact with the dielectric fluid. The sensitive part (SG1) comprises at least one pair of electrodes (E1, E2) with respective surface parts arranged at a predetermined micrometer or submicrometer distance to define at least one detection gap therebetween suitable for penetration of a part of the dielectric fluid. The sensor device has the following circuit arrangement: - means for generating an electric field between the two electrodes of the at least one pair of electrodes (E1, E2) starting from a known supply voltage, - means (V) for measuring, following the generation of the electric field, a voltage representative of a possible discharge between the two electrodes of the at least one pair of electrodes (E1, E2) through the dielectric fluid (5) present in the at least one detection gap (G).

Description

[Technical field]

[0001] The present invention generally relates to a sensor device for detecting one or more electrical quantities in a fluid, and to an electric device equipped with a sensor of the indicated type. The invention has been developed with particular attention to the detection of the dielectric strength of a dielectric fluid, preferably a fluid present in the casing of an electric device, for example a temperature regulation fluid of a battery. However, the described sensor device is also suitable for use in other fields and in combination with electric devices other than batteries. [Background technology]

[0002] In recent years, there has been a need to regulate the temperature of batteries in more efficient ways, for example batteries installed in automobiles. A technical solution adopted in some cases is to directly cool the battery cells by immersing them in a dielectric fluid in order to maximize the heat exchange efficiency. The drawback of this solution is that if the fluid in contact with the battery cells does not ensure sufficient insulation, currents can flow inside the battery pack, significantly reducing the efficiency and potentially leading to very dangerous consequences.

[0003] To manage the electrical insulating properties of the coolant directly immersing the battery cells, solutions have been proposed based on the measurement of electrical parameters such as permittivity, impedance, conductivity, etc. However, these measurements only have an indirect correlation with the actual quantity of interest represented by the permittivity, i.e. the limiting value of the electric field beyond which electrical conduction occurs through the fluid in question.

[0004] In general, fluids used in temperature conditioning of batteries should ensure a minimum dielectric strength not below a value of the order of 3 kV / mm. According to the current state of the art, direct measurement of these dielectric strength values ​​requires detection elements of macroscopic dimensions and is based on the use of voltages whose generation is very high and expensive, which may behave as a source of electromagnetic noise and may cause avalanche phenomena in relatively large areas of space, which is dangerous. On the other hand, the measurement of the electrical conductivity of the fluid alone does not always allow accurate identification of potentially dangerous situations.

[0005] For these reasons, a common approach is to measure a number of different electrical quantities, such as the aforementioned dielectric constant, impedance, and conductivity, and correlate these quantities as the measurements progress; however, the results are not always satisfactory.

[0006] Similar problems are found in applications other than those illustrated, where dielectric fluids are used in conjunction with typical electrical devices, for example for temperature regulation thereof. Summary of the Invention

[0007] The present invention is based on the consideration of the fact that a sensor arrangement based on a non-consumable case system that does not rely solely on indirect measurements or on complex correlations of indirect parameters is desirable, especially when the safety of electrical devices such as batteries is at stake.

[0008] In this context, the object of the invention is essentially to obtain a sensor device capable of detecting the degree of electrical insulation ensured by a fluid, in particular a temperature-regulating fluid, of an electrical device such as a battery.

[0009] Another object of the invention is to obtain a sensor device which operates at low voltages but is also able to detect high electrical resistivity and / or high electrical insulation of fluids.

[0010] Another object of the present invention is to provide a sensor device capable of detecting the electrical insulation of a fluid with a compact structure.

[0011] A subsidiary object of the invention is to obtain a sensor device which can be conveniently used also when it is necessary to measure the electrical insulation of materials which have very low electrical conductivity.

[0012] One or more of the above objects, as well as other objects that will become apparent hereinafter, are achieved according to the present invention by a sensor device as described below. The objects of the present invention are also achieved by an electrical device including such a sensor device. Preferred embodiments of the present invention are set forth in the appended claims. The claims form an integral part of the technical teachings provided herein in connection with the present invention.

[0013] According to the invention, a sensor device for the direct detection of dielectric strength is proposed, which sensor device has a miniaturized sensitive part for detection or is obtained in such a way that it comprises at least one pair of detection electrodes arranged in any case at a distance of micrometers or submicrometers or nanometers, generating a high electric field even starting from a low voltage, in particular the electrodes being on one and the same support, in fixed positions. In general, the sensitive part of the sensor device according to the invention comprises at least two electrodes, preferably microelectrodes, arranged at a distance between 100 nanometers and 20 micrometers, defining between them a measurement discontinuity or gap suitable for generating an electric field of several kV / m at a low voltage of approximately between 1 V and 30 V, preferably between 3 V and 10 V.

[0014] Detection can be performed using DC voltage, AC voltage of various frequencies, pulsed voltage, and voltage of various shapes.

[0015] In various preferred embodiments, the direct voltage is used to charge a capacitor with a known or predefined capacitance by means of a suitable electrical or electronic circuit, which then discharges over the measurement gap, i.e. to generate an electric field between the two electrodes. The sensor device may finally be pre-arranged with an electronic driving circuit that reverses the polarity between the electrodes at each measurement cycle, as will be described in more detail below. A possible operating scheme of the sensor device according to a possible embodiment of the invention therefore provides that a capacitor with a known capacitance is brought to a constant voltage, which is then disconnected from the power supply and connected to the sensitive part of the sensor device. By detecting the voltage across the capacitor after connection to the measurement gap of the sensitive part immersed in the fluid, it is possible to obtain a value of the dielectric strength of the fluid itself, i.e. a representative information of the degree of electrical insulation. For highly insulating fluids, the time constant is practically infinite, while the discharge of the capacitor is faster due to the conduction of the fluid. An insulating fluid such as ultrapure water has good insulating properties at low electric fields, but is highly conductive at high electric fields. It is for such types of dielectric fluids that the sensor device according to the invention is able to identify situations that cannot be measured by conductivity measurements alone.

[0016] According to another embodiment of the invention, the sensor device does not rely on the use of a capacitor, but rather its operation is resistive or based on the measurement of an equivalent resistance.

[0017] The sensitive part of the sensor device according to the invention may comprise electrode pairs arranged on one and the same support at different micrometer or submicrometer or nanometer distances, for example at distances of 2, 4, 8, 16 micrometers from each other, and independently, sequentially or simultaneously supplied with a low voltage, for example 16 V. If the time constant remains above a certain threshold for all electrode pairs, it can be concluded that the dielectric strength of the fluid is higher than, for example, 8 kV / mm. On the other hand, if a discharge is detected at the smallest measurement gap (2 micrometers in the cited example) and is significantly faster than the discharge at the other measurement gaps, it can be concluded that the dielectric strength of the fluid is comprised, for example, between 4 and 8 kV / mm.

[0018] Of course, the given examples apply in principle and the sensor device according to the invention must be calibrated according to the type of fluid to be measured, also in conjunction with the geometry of the electrodes used.

[0019] In various preferred embodiments, the electrodes of the sensitive part are obtained in the form of a thin film. The part of the shortest distance between the electrodes that defines the measurement gap can have a relatively small radius of curvature, consisting of the order of a micron or less, for example between 10 and 500 nm. Such electrodes have a pronounced "tip effect", which results in a reduction in the voltage required to obtain a partial discharge or breakdown voltage, a situation that is advantageous for the purpose of reducing the electrical voltage used in the measurement. In the case of fluids, the term "breakdown voltage" must be understood mechanically, because, given that the volume of the fluid involved in the discharge is very limited and undergoes continuous mixing due to local thermal motions and convection or even macroscopic flows, if the measurement is repeated several times, the result will in principle always be the same, unlike solid dielectrics, where no mixing occurs and the properties of the dielectric change with each discharge.

[0020] The use of thin film techniques makes it possible to achieve the precision required to obtain microelectrodes, allowing measurement gaps of micrometer, submicrometer and nanometer dimensions to be obtained. In various embodiments, the thickness of the metal film forming or constituting the electrode is comprised between 50 nanometers and 2 micrometers, preferably between 100 nanometers and 500 nanometers. Preferably, the electrode is comprised of at least two layers, for example a first layer of titanium or chromium with the function of adhesion promoter, with a thickness of 20 to 80 nanometers, and a second layer of platinum, copper, nickel or other conductor, typically with a thickness of several hundred nanometers. However, according to other embodiments, electrodes formed of a single metal, preferably chromium or titanium, can be used.

[0021] The electrodes are preferably deposited on one and the same electrically insulating support, for example made of ceramic (such as alumina or zirconia) or plastic material. In another embodiment, the electrodes can be deposited on one and the same substrate, formed of silicon oxide obtained on a silicon wafer (preferably by oxidation), the substrate having a thickness that is preferably not smaller, and preferably larger than the distance between the electrodes in the measurement gap (or in the case of a pair of electrodes, a smaller measurement gap), in order to avoid discharges inside the silicon substrate.

[0022] The preferred techniques for obtaining the electrodes are thermal evaporation and sputtering in high vacuum. Other techniques such as CVD (Chemical Vapor Deposition) and ALD (Atomic Layer Deposition) can also be used. If it is necessary to obtain very small gaps, of the order of tens to hundreds of nanometers, without using expensive lithographic techniques on the nanoscale, it is possible to obtain micrometer gaps using classical lithographic techniques and then reduce the gap by isotropic galvanic growth. In general, regardless of the deposition technique used, the definition of the electrodes is obtained by photolithographic techniques such as photoresist deposition, UV exposure, development, followed by metal or chemical attack of the metal, and removal of the photoresist. [Brief description of the drawings]

[0023] Further objects, features and advantages of the present invention will become apparent from the following detailed description, made with reference to the accompanying schematic drawings, given purely as non-limiting examples, in which:

[0024] [Figure 1] 1A to 1C are schematic perspective views from different angles of an electrical device equipped with a sensor device according to a possible embodiment; [Diagram 2] 1A to 1C are schematic perspective views from different angles of an electrical device equipped with a sensor device according to a possible embodiment; [Diagram 3] FIG. 3 is a cross-sectional perspective view of the electrical device of FIGS. [Figure 4] 3A-3C are corresponding enlarged detail views of the electrical device of FIGS. 1-2. [Diagram 5] 1 is a schematic perspective view from above of a sensor device according to a possible embodiment of the invention; [Figure 6] 1 is a schematic plan view of a sensor device according to a possible embodiment of the present invention; [Figure 7] 1 is a schematic side view of a sensor device according to a possible embodiment of the present invention; [Figure 8] FIG. 2 is a schematic rear view of a sensor device according to a possible embodiment of the present invention; [Figure 9] 1 is a schematic front view of a sensor device according to a possible embodiment of the present invention; [Figure 10] FIG. 7 is a schematic diagram of a cross section taken along axis XX in FIG. 6. [Figure 11] FIG. 8 is a schematic cross-sectional view taken along axis XI-XI of FIG. 7. [Figure 12] FIG. 2 is a schematic exploded view of a sensor device according to a possible embodiment; [Figure 13] 1A to 1C are schematic perspective views of a sensitive part of a sensor device according to a possible embodiment, viewed from different angles. [Figure 14] 1A to 1C are schematic perspective views of a sensitive part of a sensor device according to a possible embodiment, viewed from different angles. [Figure 15] FIG. 4 is a schematic diagram of a pair of electrodes of a sensitive part of a sensor device according to a possible embodiment. [Figure 16] 5A-5D are corresponding enlarged detail views of a pair of electrodes of the sensitive part of the sensor device according to a possible embodiment. [Figure 17] 11A and 11B are schematic perspective views of a sensitive part of a sensor device according to another possible embodiment, taken from different angles. [Figure 18] 11A and 11B are schematic perspective views of a sensitive part of a sensor device according to another possible embodiment, taken from different angles. [Figure 19] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Figure 20] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Figure 21] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Figure 22] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Diagram 23] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Figure 24] 15-16 of a possible alternative embodiment of an electrode pair. FIG. [Diagram 25] 4 is a simplified electrical circuit intended to illustrate a possible operating principle with capacitive driving of a sensor device according to a possible embodiment. [Figure 26] 5 is a graph showing examples of measurements performed on several types of fluids by the sensor device according to the invention; [Figure 27] Illustrates as many possible circuits of the sensor device as possible according to possible embodiments based on the capacitive driving principle of the sensitive part. [Figure 28] Illustrates as many possible circuits of the sensor device as possible according to possible embodiments based on the capacitive driving principle of the sensitive part. [Figure 29] 1 illustrates a possible circuit of a sensor device according to a possible operating mode based on the resistive driving principle of the sensitive part. [Diagram 30] A circuit equivalent to that shown in FIG. 29 is illustrated in the case of unipolar driving. [Diagram 31] A circuit equivalent to that shown in FIG. 29 is illustrated in the case of bipolar driving. [Diagram 32] 1 illustrates a possible circuit of a sensor device according to a possible embodiment, which also integrates a temperature detection function based on the capacitive driving principle of the sensitive part. [Diagram 33] 1 illustrates a possible circuit of a sensor device according to a possible embodiment, which also integrates a temperature detection function based on the resistive driving principle of the sensitive part. [Diagram 34] 1 is a schematic diagram showing a sensitive part of a sensor device according to a possible embodiment, viewed from above; [Diagram 35] FIG. 35 is a schematic cross-sectional view taken along line XXXV-XXXV in FIG. 34. [Diagram 36] FIG. 35 is an enlarged view of detail XXXVI of FIG. 34. [Figure 37] FIG. 37 is an enlarged view of detail XXXVII of FIG. 35. [Figure 38] 4 illustrates a possible circuit of a sensor device according to another possible embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Reference to an embodiment in this specification indicates that a particular configuration, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, phrases such as "in one embodiment," "in various embodiments," and the like, may be present in different places in this specification, but do not necessarily refer to one and the same embodiment. Furthermore, particular features, structures, or characteristics defined in this specification may be combined in any suitable manner in one or more embodiments, even if different from what is depicted. Numerical and spatial references used in this specification (such as "upper," "lower," "upper," "lower," etc.) are for convenience and therefore do not define the scope of protection or the scope of the embodiments. In the figures, like reference numbers are used to indicate similar or technically equivalent elements.

[0026] In Figures 1 to 4 a typical electrical device is represented diagrammatically, in combination with which a dielectric fluid is used, for example for temperature regulation purposes, and which is equipped with a sensor device according to a possible embodiment of the invention. In this example, a battery is shown with a battery pack cooled by a dielectric fluid. However, as mentioned above, the scope of the invention is not limited to this particular technical field.

[0027] The device or battery generally designated 1 has a casing 2 defining a storage volume 3, inside which electrical components are arranged, here represented as a battery pack 4 including a number of batteries or electrolytic cells 4a connected in series or in parallel. Volume 3 is suitable for receiving a dielectric fluid 5, in particular a coolant, for temperature regulation of the battery pack 4. In the following, it is assumed that the fluid 5 is a hydrofluoroether (HFE), for example a fluid belonging to the NOVEC family manufactured by 3M, Saint Paul, Minnesota, USA, or 1,1,1,2,2,3,3,3-heptafluoro-3-methoxypropane (formula: C4H3F7O - CAS Registry Number: 375-03-1).

[0028] The actual realization of possible fluid circuits and / or other components of the cooling system of the fluid 5 is irrelevant for the purposes of this specification.

[0029] One of the walls of the casing 2, in particular its side wall, is provided with a through opening 2a in which the sensor device according to the invention is placed. The opening 2a is preferably arranged at a height corresponding to the immersion of at least the sensitive end of the sensor in the fluid, in particular the at least partial immersion of the pack 4 in the fluid 5. In view of this, the device 10 may also be used as a minimum level sensor in the case of fluids with electrical insulating properties that can be distinguished from air, as will be described below.

[0030] As can also be seen in detail in figure 4, the sensor 10 is mounted in a watertight manner in the aforementioned opening 2a and is configured to allow the fluid 5 to come into contact with a sensitive part of the sensor itself, as explained below. More generally, the sensor has a sensor body configured to be mounted on an electric device or battery so that its sensitive part is in contact with or immersed in the fluid to be detected. Of course, the mounting position of the sensor 10 shown in the drawing must be understood as merely an example, since the same sensor can be mounted in other positions, provided that its sensitive part is reachable by the fluid 5 (for example along the circuit for the supply and / or recirculation of the fluid 5 in the volume 3).

[0031] A sensor 10 according to a possible embodiment is shown in different views in FIGS.

[0032] Referring initially to Figures 5-7, the sensor 10 has a first body part 11, for example made of an electrically insulating plastic material. In various embodiments, the body part 11 has a box-like portion 12 extending in the longitudinal direction and provided with a cover 12a, and a first tubular portion 13, preferably obtaining an electrical connector body. In various embodiments, the body part 11 defines a radially projecting intermediate flange 14, provided with holes 14a (Figure 8) for receiving suitable fastening elements, such as screws. Alternatively, the sensor 10 can be provided with another type of fastening and / or positioning means, such as means for a quick coupling, possibly complementary to the respective coupling and / or positioning means provided on the casing 2 of the electrical device or battery 1.

[0033] The sensor 10 preferably comprises a second body part 15, for example made of an electrically insulating plastic material. The body part 15 defines a substantially cup-shaped hollow 16 and preferably respective radially projecting end flanges 17, also provided with holes 17a (FIG. 9) for fastening means. If both are present, the flanges 14, 17 may have corresponding holes 14a, 17a of substantially the same shape and arrangement, such that in the assembled state, the holes 14a are in a position substantially coinciding with those of the holes 17a. The flanges 14, 17 may be joined to one another, for example by welding or gluing, or the mutual fastening may be achieved by using the same fastening elements, such as the aforementioned screws, used to fasten the sensor 10 in place.

[0034] In various embodiments, the sensor 10 can include elements that uniquely define an assembly position between the body part 11 and the part 15, such as, for example, a positioning element on the part 11 and a corresponding positioning counter-element on the part 15. In the illustrated example, these elements and the counter-elements are on opposite sides of the two flanges 14, 17 (see in particular the element designated 17b in FIG. 12 that protrudes axially from the flange 17).

[0035] In various preferred embodiments, the peripheral wall, preferably a substantially cylindrical wall, of the hollow portion 16 of the body portion 15 is provided externally with a seat, indicated at 16a in FIG. 12, for mounting a sealing element 18, such as an OR-type gasket. Such a gasket 18 is provided, for example, when at least a portion of the sensor 10, or at least a portion of its body portion 15, is inserted into an opening to achieve a radial seal.

[0036] In various preferred embodiments, the walls of the hollow portion 16 of the body portion 15, in particular its end or bottom wall 16a, are provided with one or more through openings, indicated at 19 (see, for example, Figures 5 and 9), for the passage of the fluid to be detected, in the non-limiting example shown, four openings 19 are provided, including a central hole and three slot-like openings, in peripheral positions relative to the aforementioned central hole. The inside of the wall 16a may be provided with a recess or depression, indicated at 19a in Figure 11, in which the inner ends of the openings 19 are located.

[0037] 8-12, the sensor 10 preferably comprises a first connection terminal, indicated at 20, which extends through a wall (indicated at 12b only in FIG. 11) separating the portions 12, 13 of the body portion 11 from one another. The first terminal 20 has a distal end portion 20a which extends inside the first tubular portion 13 and forms an electrical connector for connecting the sensor 10 to an external system. The proximal end portion 20b of the first terminal 20 instead extends into a cavity 12c (FIGS. 10 and 12) defined by the box-like portion 12 of the body portion 11.

[0038] In various embodiments, the body portion 11 also has a second connection terminal 21 passing through a wall, preferably a block portion 22 (FIGS. 10-11), which in the depicted non-limiting example extends axially beginning at the end of the box-like portion 12 opposite the tubular portion 13. The second terminal 21 has a proximal end portion designated 21a, which extends into the aforementioned cavity 12c defined by the box-like portion 12 at a position generally opposite the proximal end portion 20b of the first terminal 20. The distal end portion 21b of the second terminal 21 protrudes axially beyond the wall or block portion 22 of the body portion 11.

[0039] In various embodiments, the respective proximal end portions 20b, 21a of the terminals 20, 21 are housed in the cavity 12c and are coupled to respective connection elements of a circuit support 23 on which at least part of the control electronics of the sensor 10, in particular at least part of the electronic components necessary for detecting the dielectric strength of the fluid or the corresponding breakdown voltage, is mounted. For this purpose, said ends 20b, 21a of the terminals can be suitably shaped, for example bent and sized to fit into corresponding passages provided on the circuit support 23. The terminals 20, 21 can either extend into respective passages provided in the body portion 11 or, preferably, the body portion 11 is directly overmolded onto such terminals.

[0040] As shown in the example of Fig. 12, in various embodiments, the circuit on the support 23 has at least two connection elements 23a for connection to the sensitive part of the detection element described below via the terminals 21. This circuit can optionally provide two additional connection elements for a temperature detector, for example an NTC thermistor, arranged on the aforementioned detection element (in this case, preferably, two additional terminals 21 are provided for the connection of the temperature detector to the circuit support 23). Referring again to the example of Fig. 12, the circuit on the support 23 has three additional connection elements 23b for the terminals 20, which together with the tubular part 13 realize a connector for the external connection of the sensor 10.

[0041] It is noted, particularly from Figures 11 and 12, that in various embodiments the body portion 11 has a second tubular end 24 which extends axially from the wall or mass 22 (in the example generally opposite the first tubular portion 13) and in which the end 21b of the terminal 21 is located. The second tubular portion 24 preferably has a peripheral wall which is substantially cylindrical or, more generally, substantially complementary to the cross section of the cavity of the hollow portion 16 of the body portion 15. Preferably, the peripheral wall of the second tubular portion 24 has at least one opening 24a, preferably two openings in opposite positions, which openings allow the electrical connection, for example by welding, of said portion 21b of the terminal 21 to respective electrical connection elements (for example, indicated at 36a and 36b in Figure 12) of the detection element of the sensor 10, generally indicated at 30.

[0042] In various embodiments, the detection element 30, or its support (e.g., shown at 31 in Figs. 13-14), is arranged at the distal end of the second tubular portion 24, which for this purpose may comprise centering and / or positioning elements (two of these elements are shown at 24b in Figs. 10, 11). Said support 31 may be glued or bonded onto the tubular portion 24.

[0043] In various embodiments, in the assembled state, the tubular part 24 with the detection element 30, and possibly at least a part of the bulk part 22, are housed in a cavity defined by the hollow part 16 of the body part 15 (see for example Figures 10-11). For this purpose, preferably sealing means can be provided between the two body parts 11, 15, such as an annular gasket designated 25; for this purpose, the peripheral wall of the second tubular part 24 can be provided externally with a corresponding positioning seat, designated 24b in Figure 12.

[0044] In various preferred embodiments, further sealing means can be provided between the detection element 30 and the body part 15. In the example, for this purpose, an annular gasket, for example designated 26 in Figs. 10-12, is provided and is designed to be sealably installed between the aforementioned support part 31 (Figs. 13-14) of the detection element 30 and the wall 16a of the hollow part 16 in which the through opening 19 is arranged. For this purpose, the inner side of the wall 16a can define a corresponding positioning seat (not shown) for the gasket 26. As can be imagined, the annular gasket 26 together with the respective part of the wall 16a and the aforementioned support part 31 of the detection element 30 defines - on one side - a detection chamber, not shown, into which the opening 19 and possible recess 19a open and into which - on the other side - a sensitive part (described below) of the detection element 30 faces.

[0045] A possible embodiment of the sensing element 30 is shown in FIGS.

[0046] The sensing element 30 comprises a support 31, preferably made of an electrically insulating material, for example ceramic or plastic. With further reference to the illustrated non-limiting example, the support 31 preferably has a rectangular or polygonal peripheral profile (here substantially octagonal) and is provided with a through hole 32. This shape and the presence of the through hole 32 are not essential and the shape can be different, for example circular.

[0047] The upper surface of the support 31 is provided with SG 1 In the present invention, there is a sensitive part, denoted by E1 and E2, which comprises at least one pair of electrodes, in particular microelectrodes, on a support, denoted by E1 and E2.

[0048] The electrodes E1, E2 are preferably in the form of thin films. As already mentioned, in various preferred embodiments, the thickness of the metal film from which the electrodes E1, E2 are obtained is comprised between 50 nanometers and 2 micrometers, preferably between 100 and 500 nanometers. The electrodes E1, E2 can be made of at least two layers of different metallic materials or of a single layer of metallic material. In the following, it is assumed that both electrodes E1, E2 are formed by respective layers of platinum and chromium on a support 31, the platinum forming the upper layer and the chromium the lower layer.

[0049] The electrodes have respective portions set at a minimum or predetermined distance between them, comprised of micrometer or sub-micrometer or nanometer distances, preferably between 100 nanometers and 20 micrometers, to define a constant measurement gap therebetween.

[0050] In what follows, it is assumed that the two electrodes E1, E2 are at a distance of approximately 2 microns at their respective closest points to each other.

[0051] In the illustrated, non-limiting case, the upper surface of the support 31 is provided with first conductive tracks, indicated in FIG. 13 as 33a, 33b, for example screen-printed tracks of a metallic material or a conductive paste, which are electrically connected with similar conductive tracks, indicated in FIG. 13 as 34a, 34b, provided on the lower surface of the support 31. The upper tracks 33a, 33b can each extend from the respective electrode E1 or E2 to a respective through-hole in the substrate 31, here indicated as 32a, 32b, which is filled or covered on its surface with a conductive material and which is contacted by the material of the track 33a or 33b. Similarly, the lower tracks 34a, 34b are in contact with the material filling or covering the respective hole 32a or 32b, and extend from there to a respective contact pad 35a or 35b, respectively, made of a conductive material, which in turn connects the sensing element 30, i.e. the sensitive part SG 1From these start the connecting elements 36a and 36b of the electrodes E1 and E2. The elements 36a and 36b may, for example, be represented by electrical conductors, possibly flexible ones.

[0052] As mentioned above, a temperature detector such as an NTC thermistor is connected to the RT 1 2. It can be mounted on the support 31, for example on its underside, as illustrated in FIG. 2. In this case, at least two additional connection elements or conductors for this detector also extend from the support 31 for the purpose of connecting it to the control electronics via suitable terminals 21.

[0053] With reference to Figures 15-16, in various preferred embodiments, at least one of the electrodes (here electrode E1) has a generally pointed portion of its respective peripheral profile, indicated by E1a, designed to face a corresponding portion (E2b) of the peripheral profile of the other electrode (here electrode E2) at a predefined or minimum distance, in order to define a measurement gap, indicated by G in the detail of Figure 16. The portion with the short distance between electrodes E1 and E2 can have a relatively small radius of curvature, of the order of microns, in the corresponding pointed profile portion. The choice to provide at least one electrode with a pointed portion aims to exploit the so-called "tip effect", which makes it possible to use low voltages, in particular below 50 V, to obtain partial discharge or breakdown voltages in the portion with the smallest distance between the two electrodes. In the examples shown in Figures 13-16, only electrode E1 has a pointed shape, but as will be explained later, this is not an essential feature.

[0054] As mentioned above, the sensor of the invention is adapted to carry out a detection aimed at determining the possibility of losses by conduction in a fluid that is ideally insulating but that may partially lose this property under certain conditions. In other words, it makes it possible to directly deduce the possible decay of the dielectric strength of a dielectric fluid relative to an initial or nominal value or range of nominal values, in particular below a safety threshold.

[0055] The principle of this sensor is that a high electric field can be obtained even with a very small distance between the electrodes. This phenomenon is due to the fact that a stronger electric field is formed in areas of the conductor surface with a small radius of curvature, since the electric field is inversely proportional to this radius. When a tip is present, the radius of curvature is ideally zero, and as a result, the electric field is ideally infinite.

[0056] In reality, it is impossible to make the radius of curvature zero, but if there exists a tip with a very small radius of curvature (micrometers or submicrometers), even if it is not zero, it is possible to obtain an electric field of tens of kV / cm even with a potential of a few volts. Thus, by using electrodes with a shape that defines the tip, such as electrode E1, and a second electrode with a flat shape facing the tip, such as electrode E2 (which can have a different shape, as will be described later), placed at a sufficiently small distance, it is possible to obtain a current flow due to the corona effect (a phenomenon that occurs when there are two conductors with a high potential gradient, and the ionization caused by the presence of a high electric field causes a current to flow in the fluid in which these electrodes are immersed). The high electric field is obtained both by the pointed shape of one or both electrodes and by the close distance between the two electrodes. It should also be noted that the very thin thickness of the film contributes to an increase in the local electric field, even more than in a pattern on a plane. A further advantage of limiting the facing area of ​​the two electrodes is that it confines any potential discharge to a limited, well-spaced volume.

[0057] Thus, for example, by placing two electrodes E1, E2 immersed in the fluid to be measured in parallel to a capacitance charged at an appropriate voltage level - depending on the fluid to be detected and / or the minimum distance between the electrodes (i.e. the characteristic size of the detection gap) - it is possible to determine the level of degradation of the fluid based on the residual voltage level measured on the capacitance after a predetermined time interval.

[0058] The lower the voltage level and the higher the current between the electrodes, the more the fluid has lost its insulating properties. Therefore, the residual voltage level on the capacitor after a given time can be correlated with the insulating properties of the fluid and its dielectric strength can be inferred.

[0059] 17 and 18 show a possible alternative embodiment of the detection element 30, in which a support 31 - here having a circular shape and made, for example, of glass fibre and epoxy resin (vetronite) or other material suitable for printed circuit boards or PCBs, or of alumina - is deposited on a substrate 31a made of silicon oxide obtained on a silicon wafer 31b, on which the sensitive part SG of the detection element 30 is deposited. 1 In order to form the electrode pair E1-E2, a plurality of pairs of electrodes E1-E2 are defined.

[0060] Each pair of electrodes E1, E2 may define a detection gap having a different amplitude, for the reasons explained above.The substrate 31a preferably has a thickness that is not less than, but preferably greater than, the distance between electrodes E1 and E2 at the smallest measurement gap.

[0061] In an embodiment, the various electrodes E1, E2 are connected to the respective connecting conductors 36a, 36b by wire bonding, preferably via microwires 37a, 37b based on noble metal. However, in this embodiment, the microwire 37b of the electrode E2 is connected to a common pad, indicated in Fig. 18 as 35b, from which a single connecting conductor 36b starts. Thus, in this embodiment, the detection element 30 comprises only three connecting conductors (without prejudice to the possibility of the additional presence of the aforementioned temperature detector, in which case at least one additional conductor, preferably at least two additional conductors, are provided).

[0062] In embodiments of the type shown in Figures 17-18, the use of a silicon wafer makes it possible to obtain a highly doped region which can be used as a gate electrode to modulate partial discharges between the sensing gaps of a pair of electrodes, or of each pair of electrodes E1-E2, when it is desired to obtain particularly fine measurements of transport phenomena within a fluid, for example by giving the sensor a higher selectivity with respect to a particular contaminant.

[0063] The polarization of fluid molecules can indeed modify their electrical conduction. From this point of view, a phenomenon that can be exploited is the pronounced electronegativity of the fluorine atoms present in the molecules of fluids commonly used for insulating and cooling batteries, such as hydrofluoroethers (HFEs), e.g. 1,1,1,2,2,3,3,3-heptafluoro-3-methoxypropane.

[0064] During the discharge between the electrodes E1-E2, the fluorine atoms tend to segregate the free electrons, which is one of the reasons why this type of fluid has a relatively high breakdown voltage. The presence of a gate voltage affects the polarization of the molecules and can create different paths that promote or hinder the discharge depending on the value and polarity of the gate voltage. Thus, by measuring the current between the main electrodes (for example, the electrodes with the "tip" or "tip-plane" become the source and drain) as a function of the gate voltage, the detection of different contaminants can be obtained, with appropriate mapping.

[0065] A further advantage of using a substrate 31a at least partially in silicon is that the sensitive portion SG 1 The driving circuitry, or at least part of said circuitry, can be directly integrated into the substrate.

[0066] As mentioned above, in both cases it is possible to use an insulating support or substrate, on whose surface one or more pairs of electrodes E1-E2 are deposited directly or in some other way to obtain a suitable gate electrode, on which an insulating layer (for example a polymer layer having a thickness of a few microns, for example 2-10 microns) is deposited and on which at least one pair of electrodes E1-E2 through which the discharge is carried out is formed. Examples of this type are described with reference to Figures 34-38.

[0067] Sensitive part SG of detection element 30 1 comprises several pairs of electrodes E1-E2, the measurement gaps supplied with one and the same voltage can be separate, as in the case of FIG. 17, or the two electrodes E1 and E2 can be operated in parallel at the same voltage and the same distance to define several measurement gaps therebetween, as in the case of FIG. 23, to provide redundancy and to avoid malfunctions (gas bubbles or impurities in the gap, etc.).

[0068] 19-20 show possible alternative shapes of the two electrodes E1-E2, distinguished by pointed portions E1a, E2b of their respective peripheral profiles. Such embodiments may be advantageous, for example, for maximizing the local electric field.

[0069] 21-22 show further possible alternative shapes of the two electrodes E1-E2, where the peripheral profile of the electrode E1 has an axially extending protruding portion E1a, which is inserted between two extending parallel portions of the shaped portion E2b of the peripheral profile of the electrode E2. Such an embodiment is advantageous, for example, for improving the homogeneity of the chemical attack process of thin films during the manufacture of microelectrodes.

[0070] 23-24 show a further possible alternative shape, in which the facing parts of the peripheral profile of the two electrodes E1-E2 have a substantially interdigitated shape, i.e. successive projections E1a of the electrode E1 are received in successive recesses E2b of the electrode E2. As already mentioned, such an embodiment is advantageous for defining several equal measurement gaps, operating in parallel, by only two electrodes, for example for reasons of redundancy and to avoid occasional malfunctions due to external causes such as air bubbles or impurities in a single gap. Although in this case the value of the electric field at the same applied voltage and the same minimum distance between the electrodes may be reduced than in the "tip-to-plane" or "tip-to-tip" cases, this embodiment may be advantageous, for example, in the case of fluids with a higher conductivity, because they are contaminated and / or degraded, and may ensure a higher robustness of the electrodes, which are less susceptible to damage by the electric field itself applied during discharge.

[0071] The sensor 10 is mounted such that its body portion 15 is at least partially exposed (at least at its wall 16a) to the fluid to be detected, for example as illustrated in FIGS.

[0072] In this way, part of the fluid 5 can penetrate through the through opening 19 and reach the detection chamber separated between the sealing element 26, the inside of the wall 16a and the support 31 of the detection element 30, and since the sealing element 26 surrounds the area of ​​the upper surface of the support 31 in which at least one pair of electrodes E1-E2 are arranged, both electrodes are in contact with the fluid 5.

[0073] FIG. 25 shows a schematic of a possible operating principle of the sensor 10, where Vdc denotes a low voltage source, S1 and S2 denote two switches (preferably of electronic or controllable type), C denotes a capacitor of known or predefined capacitance, and SG 1 denotes a sensitive part having at least two electrodes of the type previously indicated by E1 and E2. OS denotes a detection device or instrument, such as an oscilloscope. The sensor is mounted in such a way that the fluid to be detected bathes the electrodes E1-E2 and therefore also penetrates the detection gap G, as previously described.

[0074] By closing switch S1, the capacitor C is charged with the voltage Vdc. Then, switch S1 is opened and switch S2 is closed, and the sensing part SG 1 Discharge the capacitor C over the measurement gap defined between the electrodes.

[0075] The graph of Fig. 26 shows typical discharge trends for several types of fluids detected by the applicant with a sensor device according to the invention, operating according to the principles described above. The tests were carried out with a DC voltage of 5V, a capacitor C having a capacitance of 100 nF, and a sensitive element SG having electrodes E1 and E2 made of chrome having a shape of the type shown in Fig. 15. 1 , and a detection gap G of 2 micrometers. The graph shows time t (seconds) on the horizontal axis and voltage U (volts) on the vertical axis.

[0076] For example, Novec 7100® is one of the fluids commonly used for temperature conditioning of electrochemical cells in batteries. The discharge depicted is substantially identical to that of air (the two curves on the graph are substantially indistinguishable), with a time constant related to a 100 nF capacitance on a 10 MOhm resistance (the internal resistance of the oscilloscope OS used).

[0077] The same fluids as in the graph of Figure 25 were also analyzed with a dielectric strength meter, a typical instrument used to measure the dielectric strength of materials, and the corresponding results are shown in Table 1 below.

[0078] Table 1 TIFF2024534490000002.tif31140

[0079] The dielectric meter was able to measure the discharge voltage of ultrapure water at about 2.4 kV / cm, but a benchtop conductivity meter with sensitivity down to nS / cm was unable to measure the conductivity. This is because ultrapure water is conductive in the presence of a high electric field due to localized charge generation, not due to free charges already present in the fluid. As can be seen from the graph in Figure 26, the curve for ultrapure water is well distinguished from both the Novec curve and the curves for less pure water (deionized water and tap water).

[0080] The sensor according to the invention can be manufactured according to different circuit variations, either capacitive or resistive.

[0081] 27 is a principle diagram of unipolar drive of the sensor 10, e.g., in relation to the capacitive operation described above. Only the essential components useful for understanding the operation are shown in this diagram, namely: -SG 1 shows diagrammatically the sensitive part in which the electric field occurs in the measurement gap G and which consists of a pair of electrodes E1-E2 of the type described above or possibly of several pairs of electrodes connected in parallel to one another. -C 1 denotes a capacitor realizing the capacitance for measuring the residual voltage. -V d is the capacitor C 1 The arrows indicate the voltages across the -V 1 indicates a typical constant voltage source. -V is the capacitance of the capacitor C 1 The voltage level V d This refers to a system or device that can measure. -SW 1 , S.W. 2 , S.W. 3 indicates a typical control switch.

[0082] Not necessarily all switches 1 , S.W. 2 , S.W. 3may not necessarily be present and may be located in a slightly different circuit location than illustrated. 1 Capacitance value of power supply V 1 The voltage supplied from and the characteristic size of the sensing gap (the minimum distance between electrodes E1, E2) are selected according to the type of fluid to be sensed.

[0083] According to the priority control method, at time T 0 Switch SW 1 is open, and the switch SW 3 is open, and the switch SW 2 is closed, and the capacitor C 1 Terminal voltage V C becomes 0V.

[0084] Later time T 1 In the switch SW 2 opens and the switch SW 1 is closed, and the switch SW 3 In this way, the capacitor C 1 Voltage V d V 1 (V d ≒V 1 ).

[0085] Later time T 2 In the switch SW 2 The switch SW is always open. 1 is opened and the switch SW 3 is closed.

[0086] Later time T 3 After a certain known time interval, the capacitor C 1 Voltage V d is measured using a detection device V. The level of the measured voltage is directly correlated to the insulating properties of the fluid, and therefore the measurement cycle lasts for a period of time T 0With this type of configuration, if the residual voltage measured at the capacitor terminals falls below a predefined threshold, it can be presumed that the dielectric strength of the fluid is no longer sufficient to allow safe use of the capacitor, and therefore the fluid itself, and an appropriate alarm signal can be activated accordingly.

[0087] Switch 1 and S.W. 2 It should be noted that the switch SW forms a so-called half-bridge structure and can easily be obtained by means of individual transistors, or an integrated circuit customized for this function, or by means of a push-pull output of a common microcontroller or integrated circuit. 3 can be obtained by means of relays, integrated analog switches, FET transistors, or other systems suitable for this purpose.

[0088] In another version, the switch SW 3 It is also possible to design the drive in such a way that the presence of is omitted. In this case, the circuit is simplified and the cost and size are reduced accordingly. The disadvantages are that the current consumption is higher and the deterioration of the electrodes E1-E2 may be faster.

[0089] Switch 2 can be omitted, but in this case it is common to remove the capacitor C 1 However, this is not a concern in bipolar applications of sensor 10. However, the usefulness of sensor 10 in bipolar applications is evident as follows.

[0090] 28 is a principle diagram of the bipolar drive of the sensor 10, always in conjunction with the capacitive method described above, and in this case the diagram highlights only the essential features that are useful for understanding the operation.

[0091] SG 1To improve the durability of the detection element, bipolar drive, i.e., capacitor C 1 Voltage V at the terminals of d It is possible to use a drive such that the electric field generated between the two electrodes E1-E2 is 1 V present in d Depending on the voltage, the polarity changes, so that the deposition effects due to the galvanoplastic effect on the electrodes can be minimized. To obtain this type of drive, a so-called "full bridge" structure is used, as shown in the principle diagram of Figure 28, where the SG 1 , C 1 , V d , V 1 The components indicated by and V are similar to those described with reference to FIG.

[0092] SW 1 , S.W. 2 , S.W. 3 , S.W. 4 , S.W. 5 and S.W. 6 Typical control switches are shown, and again, not all may be present and may be located in slightly different circuit locations than illustrated.

[0093] According to the priority control method, at time T 0 In the switch SW 1 , S.W. 3 , S.W. 5 , S.W. 6 opens and the switch SW 2 is closed, and the switch SW 4 Also closes the capacitor C 1 Terminal V d Set the voltage level to 0V.

[0094] Note that the condition of keeping the capacitor at 0 V can be omitted, that is, at time T 0 The state of the circuit at is arbitrary.

[0095] Later time T 1 Switch SW2 Open the switch SW 1 By closing the switch and maintaining the other switches in their normal state, the capacitor C 1 Voltage V d V 1 (V d ≒V 1 ).

[0096] Later time T 2 In the switch SW 1 is opened and the switch SW 5 and SW 6 is closed and the other switches are kept in their normal states. 5 and S.W. 6 The condition for closing the switch SW may be omitted. 5 and S.W. 6 may not be present, or the sensitive part SG 1 The electrodes E1 to E2 of the capacitor C 1 may be connected in parallel to the

[0097] Later time T 3 At this time, i.e. after a predetermined known time interval, the switch SW 5 and S.W. 6 If there is a capacitor C 1 The above voltage is measured using device V. As described for FIG. 28, the measured voltage level directly correlates to the insulating properties of the fluid and is transmitted as output data from sensor 10.

[0098] Subsequent time T 4 In the switch SW 2 is closed, and the state of other switches, especially switch SW 4 The closed state of the capacitor C 1 The voltage at the terminals of V d The level becomes 0V.

[0099] Later time T 5 So, switch SW 4 is opened and the switch SW 3is closed and the other switches are maintained in their original state, resulting in a current flowing through the capacitor C 1 V d Voltage is -V 1 (V d ≒-V 1 ) at a level equal to

[0100] Later time T 6 So, switch SW 3 is opened and the switch SW 5 and SW 6 and are closed, and the states of the other switches are maintained. As mentioned above, the switch SW 5 and SW 6 The closing of the electrodes E1 to E2 can be omitted or can be made nonexistent, and the electrodes E1 to E2 can always be connected to the capacitor C 1 can also be connected in parallel.

[0101] Later time T 7 At this time, i.e. after a predetermined known time interval, the switch SW 5 and S.W. 6 If there is a capacitor C 1 Again, the measured voltage level directly correlates to the insulating properties of the fluid and is transmitted as output data from the sensor 10.

[0102] The measurement cycle begins at time T 0 It will start again from

[0103] Switch 1 -SW 2 and S.W. 3 -SW 4 forms the aforementioned "H-bridge" structure (full bridge), which again can be easily obtained by means of discrete transistors, or integrated circuits dedicated to this function, or by means of the push-pull output of a general microcontroller or integrated circuit. Also in this case, the switch SW 5 and SW 6 may be obtained by means of relays, integrated analog switches, FET transistors, or any other system suitable for the purpose.

[0104] As can be seen, according to the principle diagram of Figure 28, the bipolar capacitor C 1 Upper V d That is, the driving of the capacitor C 1 It is possible to reverse the voltages on the terminals or drive both positive and negative on the same terminal.

[0105] In an embodiment of the type described with reference to Figures 25, 27 and 28, the representative voltage measured varies as a function of the discharge time of the capacitor. A capacitor discharges for two reasons: either the resistance of the measurement circuit is not zero (this is unavoidable in a real circuit) and as a result a current flows in the circuit, or a current flows between the two electrodes of the detection gap. Above a certain threshold, discharge occurs, resulting in a current between the two electrodes due to an increase in charge carriers, which leads not only to the corona or "tip" effect described above, but also to the dissociation of new charge carriers (electrons and positive ions) in the fluid. Whether the capacitor discharges slowly or suddenly depends on the relative values ​​of the capacitance and the current in the detection gap. For illustrative purposes, a 100 nF capacitor charged with a voltage of 5 V requires an average current of 0.5 μA to be fully discharged in 1 second. This means that a current of about 500 A / cm2 will flow through a detection gap of the type considered here. 2 This corresponds to a current density that can be estimated as: and is certainly not a small current density for a fluid that must be considered an insulator.

[0106] The actuation principle described with reference to Figures 25, 27 and 28 can be defined as "capacitive" since it uses the discharge of a capacitor to provide a defined amount of charge to the sensing gap G. However, according to other embodiments of the invention, it is possible to use a fully resistive system for both unipolar and bipolar actuation. An example in this sense is shown in Figure 29, where only the essential components useful for understanding the operation are highlighted. Also in Figure 29, SG 1 , V 1 , V are the same as those described with reference to Figures 27 and 28. In Figure 29, -SW XL and SW XH-X , where x ranges from 1 to 4, typical control switches are shown, again not all of which may be present and may be located in slightly different circuit locations than illustrated. -R RX , where X is 1 to 4, shows the reference resistor through which the resistor divider is obtained to calculate the various SW XH and SW XL Through the switch, the sensing part SG 1 are alternately connected to -V SG is the sensing part SG 1 The voltage between the two electrodes E1-E2 is shown, and the arrow indicates its direction.

[0107] Here, a system or device V is configured to measure the voltage level of a node designated N.

[0108] The principle of operation is that of a voltage divider: the detection gap is placed in series with another resistor R (the value of this resistor can be varied with more resistors and appropriate circuit configurations, as will be described later). When a voltage is applied across the detection gap, connected in series with some resistor R, the potential of node N is zero (ground) in the absence of current, so that the full voltage V 1 This voltage V 1 is sufficient to generate a current through the sensing gap, the potential of N changes by a value V(t) = Ri(t) and stabilizes at a value V. This configuration allows us to define an equivalent resistance of the gap, as described in more detail below.

[0109] In the illustrative example, four reference resistors R R It should be noted that although the present specification refers to a system using a 10-V supply, the circuit can be extended to more resistors or reduced to a fewer number.

[0110] Again, preferably, resistor R R Resistor values ​​and their numbers, power supply V 1The voltage supplied from and the characteristic dimensions of the detection gap (the minimum distance between the electrodes E1, E2) are selected according to the type of fluid to be detected.

[0111] Referring to the diagram in FIG. 29, in the case of unipolar driving, the following two cases are considered. 1) Switch 1L From SW 4L and switch SW 5H does not exist, and the switch SW 5L is replaced by a short circuit or is always closed; switch SW 1H From SW 4H are alternately closed one by one and the voltage at node N is measured after the settling time. 2) Switch 1H From SW 4H and switch SW 5L does not exist, and the switch SW 5H is replaced by a short circuit or is always closed; switch SW 1L From SW 4L are alternately closed one by one and the voltage at node N is measured after the settling time.

[0112] Referring to FIG. 29, in the case of bipolar driving, the following two cases similar to those described above are also possible. 1) Switch 1L From SW 4L and switch SW 5H Open the switch SW 5L is always closed; switch SW 1H From SW 4H are alternately closed one by one and the voltage at node N is measured after the settling time. 2) Switch 1H From SW 4H and switch SW 5L Open the switch SW 5H is always closed; switch SW 1L From SW 4L are alternately closed one by one and the voltage at node N is measured after the settling time.

[0113] It can be easily assumed that the equivalent circuits shown in Figures 30 and 31 can be obtained in both the case of unipolar drive and the case of bipolar drive.

[0114] With unipolar drive, only one of two cases exists for each measurement cycle, depending on which configuration is selected, whereas with bipolar drive, the two circuit configurations, determined by the switch state, alternate between one measurement cycle and the next.

[0115] This so-called "proportional" method allows measurements to be made while always keeping the reference of the measurement system the same.

[0116] For convenience, but not limited to, consider using 0V as the reference. In this case, in case 1), the voltage V SG is the sensitive part SG 1 (Fig. 30), whereas in case 2) the voltage VR X is the resistance R RX The voltage is measured at the terminals of the

[0117] In addition, in case 2), if the same arrangement as in case 1) is maintained, the sensitive part SG 1 Voltage V at terminal SG becomes negative, which means that in Figures 30 and 31, SG 1 From a physical point of view, the sensing element SG is the same as the capacitive type described above. 1 An inversion of the electric field at the terminals is obtained.

[0118] In case 1), the sensitive part SG 1 The equivalent resistance R for the two terminals of the electrodes E1-E2 SG is given by the following formula: TIFF2024534490000003.tif10150

[0119] In case 2), the sensitive part SG 1 The equivalent resistance to the terminals of the two electrodes E1-E2 is instead given by the following equation: TIFF2024534490000004.tif11150

[0120] Referring to the example of Figure 29, note that electrode E2 is at a fixed potential V. As a result, the voltage at node N, whether measured with respect to ground or with respect to V, will be absolutely equal and less than a known constant represented by the voltage V. The above is therefore equivalent.

[0121] In order to ensure that the sensor 10 operates correctly over the entire temperature range provided by the application, the sensitive element SG 1 Temperature measurement may also be used through a suitable temperature detector placed near the As mentioned above, such a temperature detector may include an NTC type thermistor.

[0122] Through temperature detection, the capacitor C in Figures 27-28 1 A correction by a suitable compensation polynomial of degree 1 or higher may be applied to the voltage level measured at the terminals of, or to the equivalent resistance measured by the proportional method referred to in Figures 29 to 31. For the purpose of determining the coefficients of the compensation polynomial, two or more measurements of the voltage level or resistance may be made, for example at different known temperatures in the reference fluid.

[0123] FIG. 32 shows a simplified diagram of an implementation that may be used to obtain a sensor 10 based on a capacitive approach with bipolar drive and with temperature detection for compensation purposes.

[0124] Passive and protection components necessary for the circuit to operate correctly are omitted, and the SG 1 , C 1 , and V d The elements are similar to those described above, and therefore have the following basic elements: -RT 1 A temperature detector is shown at and is placed near electrodes E1-E2 and is used to perform temperature compensation. -SW 1 , S.W. 2 , S.W. 3 , S.W. 4The switch is of the type already mentioned above, in particular in relation to FIG. 28, and can for example be obtained via two outputs of GPIO type (General Purpose Input / Output) of an arbitrarily configurable general-purpose microcontroller. -V SNS is the capacitor C 1 denotes a typical constant voltage source to which is charged, i.e., the drive voltage of the sensor 10. -OA 0 and O.A. 1 In the figure, two op-amps are shown, with a measurement capacitor C 1 is used as a voltage tracker to isolate it from the input of the acquisition system and ensure a very high input impedance (the acquisition system means the part excluding the circuitry from the electrodes E1-E2 to the converter ADC). -ADC is a generic analog-to-digital converter. -ADC MUX denotes a general purpose multiplexer, which is set between the input of the quantity to be acquired and the converter ADC. -D&AC (Drive & Acquisition Control) indicates blocks representing the control algorithm of the drive system, the ADC MUX multiplexer, and the ADC converter. -C&C (Computation & Communication) shows blocks representing the temperature compensation algorithm, the calculation of the measurement values, and the communication protocol.

[0125] Preferably, the switch SW 1 , S.W. 2 , S.W. 3 , and S.W. 4 The control algorithm of is similar to that described with reference to Fig. 28 for the bipolar drive of the sensor 10. The part previously indicated by V, i.e., the measurement system or device, is now an operational amplifier OA 0 and O.A. 1 It consists of a multiplexer ADC MUX and a converter ADC.

[0126] During operation, capacitor C 1During two consecutive measurement cycles of the upper voltage level (inputs 0 and 1 of the multiplexer), the detector RT 1 Temperature sensing (input 2 of the multiplexer) is performed via the capacitor C 1 , it is necessary to carry out the corresponding compensation as described above, based on the aforementioned polynomial, at the voltage levels measured at the terminals of

[0127] FIG. 33 shows a simplified scheme of a possible implementation that can be used to obtain a sensor 10 with temperature detection for compensation purposes, based on a resistive or proportional approach with bipolar drive as described above.

[0128] In this case too, the passive and protective components are omitted, which are in any case necessary for the correct operation of the circuit, and the element SG 1 Considering that is similar to that described above, the following basic elements exist: -RR 1 , R.R. 2 , R.R. 3 and R.R. 4 With particular reference to FIG. 29, with a reference resistor of the type shown above, four voltage dividers are obtained which operate at different measurement ranges in order to optimize the accuracy of the sensor 10. RT 1 indicates a temperature detector, which is placed near the measurement electrodes E1-E2 and is used for performing temperature compensation. -SW 1H , S.W. 2H , S.W. 3H , S.W. 4H , S.W. 5H , and S.W. 1L , S.W. 2L , S.W. 3L , S.W. 4L , S.W. 5L With particular reference to FIG. 29, the switches already mentioned above are shown, which can be obtained through corresponding GPIO outputs of an optionally configurable general-purpose microcontroller. -V SNS 1 shows a typical constant voltage source for driving the sensor 10. -OA 0is an op-amp used as a voltage tracker to isolate the voltage divider from the measurement system and ensure very high input impedance. -ADC stands for general-purpose analog-to-digital converter. -ADC MUX denotes a general purpose multiplexer, which is placed between the input of the quantity to be acquired and the converter ADC. -D&AC (Drive & Acquisition Control) indicates blocks representing the control algorithms of the drive, the multiplexer ADC MUX and the converter ADC. -C&C (Computation & Communication) is a block that represents the correction algorithm, calculation of measurement values, and communication protocol.

[0129] Switch 1H , S.W. 2H , S.W. 3H , S.W. 4H , S.W. 5H and S.W. 1L , S.W. 2L , S.W. 3L , S.W. 4L , S.W. 5L The control algorithm of is the same as that described with reference to FIG. 33 for the bipolar drive of the sensor 10. In this case, too, the part previously indicated by V is replaced by an operational amplifier OA 0 It is composed of a multiplexer ADC MUX and a converter ADC.

[0130] In operation, again as explained in relation to FIG. 29 (input 0 of the multiplexer), between two successive measurement cycles, the detector TR 1 (input 1 of the multiplexer) and it is necessary to carry out the corresponding compensation as described above, based on the polynomial described above, for the measured equivalent resistance.

[0131] In order to compensate for temperature variations as well as construction and assembly tolerances, the sensor according to the present invention may be calibrated. If the sensor 10 performs temperature sensing, then prior to calculating the coefficients of the temperature compensation polynomial, the sensor must be calibrated, which may be done according to known techniques per se.

[0132] The acquisition system (as mentioned above, the sensor element SG 1 (including the part of the circuit between the converter and the ADC excluded) at a given stable temperature, the capacitor C 1 The capacitance can be calibrated using a reference sample resistor (and therefore of precisely known value) set in parallel with the capacitance of the sensor 10 to determine the actual value of the capacitance input to the acquisition system through measurement of the time constant RC of the circuit. The measured capacitance value is stored in non-volatile memory inside the sensor 10 and used to perform the appropriate calibration of the measurements.

[0133] Calibration of the acquisition system can also be performed in the case of sensors operating according to the resistive or proportional law (Figures 29-31 and 33).

[0134] Sensing section SG 1 is calibrated while connected to the acquisition system. In this case, the capacitor C 1 One or more measurements of the above residual voltage levels are made with reference sample fluids at a predetermined stable temperature to determine the variance relative to the expected nominal value. This information is stored in non-volatile memory within the sensor and used to properly calibrate the measurements.

[0135] Sensing section SG 1 Calibration of can also be performed in the case of sensors operating according to the resistive or proportional law (Figures 29 to 31 and 33).

[0136] As shown above, the sensitive part SG 1 A pair of two electrodes E1 and E2 - or each pair - present in the sensitive part SG can be operatively associated with a third electrode performing a source function and a gate function, the third electrode performing a gate function. 1If the electrode comprises a silicon wafer, the aforementioned third electrode can be obtained by appropriately doping a portion of this wafer. Figures 34 to 37 show instead a sensitive part SG with electrodes E1 and E2 of the type already described. 1 37, an electrode E3 with a corresponding connecting track E3a can be obtained on the substrate 31, which is then covered with a layer of dielectric material 31c on which the electrodes E1 and E2 are arranged.

[0137] Fig. 38 illustrates a possible circuit arrangement including the third electrode E3 mentioned above. In the illustrated case, for simplicity, the circuit shown is very similar to the circuit of Fig. 27, i.e., the switches SW 1 and S.W. 2 27, but the concept is obviously transferable to the other circuits described. In comparison with FIG. 27, in FIG. 38, the gate electrode E3 is driven by SW 4 and SW 5 There is an additional switch denoted by and associated circuit branch.

[0138] Referring to the example in Figure 38, the switch SW 1 and S.W. 5 With the switch SW open, 4 It is possible to polarize the gate electrode E3 by closing the capacitor C 1 After charging, switch 3 When closed, a voltage is applied across the gap in the presence of a polarization of the gate electrode E3.

[0139] The features of the present invention as well as its advantages will be apparent from the given description.

[0140] It will be clear to a person skilled in the art that numerous modifications are possible to the sensor arrangement described by way of example without departing from the scope of the invention as defined in the appended claims.

[0141] It has already been mentioned that it is possible to use the sensor 10 "indirectly" as a minimum level sensor. Such a use can be envisaged, for example, in applications where the electrical parts of a typical device must always be at least partially immersed in a fluid lower than air and having clearly distinguishable electrical insulating properties, for example in arrangements of the type shown in figures 1 to 4 in connection with batteries. It will be understood that in normal operation, with the sensitive part of the sensor 10 in contact with the fluid 5, the sensor itself provides output information related to a certain value of the dielectric strength of the fluid 5, which may vary within certain limits (depending on possible decay of the insulating properties), but which is always clearly distinguishable from the value of the dielectric stiffness of air.

[0142] Based on this, if the sensor 10 detects a dielectric strength value similar to air, it is inferred that the level of the fluid 5 has dropped below the sensor installation location and corrective action is initiated, such as an alarm signal or initiation of an automatic fluid refill system.

Claims

1. A sensor device for detecting the dielectric strength of a dielectric fluid, the sensor device (10) comprising a sensitive part (SG) designed to be in contact with the dielectric fluid. １ a sensor body (11, 15) supporting the sensor; Sensing part (SG １ ) comprises at least one pair of electrodes (E1, E2) having respective surface portions (E1a, E2b) set at a predetermined micrometer or sub-micrometer distance from each other to define at least one detection gap (G) therebetween through which a portion of the dielectric fluid (5) can penetrate, The sensor device (10) comprises the following circuit arrangement: - means (V) for generating an electric field between two electrodes of at least one pair of electrodes (E1, E2), starting from a known or predetermined supply voltage; １ , S.W., C. １ ;V １ , S.W., R;V. １ , S.W., C. １ , O.A. ０ , O.A. １ , ADC MUX, ADC;V １ , S.W., R., O.A. ０ , ADC MUX, ADC), and - a representative voltage (V) representing a possible discharge between two electrodes of at least one pair of electrodes (E1, E2) through the dielectric fluid (5) present in at least one detection gap (G) following the generation of the electric field; Ｃ ;V ＳＧ ;V ＲＸ (V), A sensor device having the following:

2. 2. The sensor device according to claim 1, wherein the surface portions (E1a, E2b) of the two electrodes of at least one pair of electrodes (E1, E2) are at a distance from each other comprised between 100 nanometers and 20 micrometers.

3. 2. The sensor device according to claim 1, wherein the circuit arrangement is configured to generate, between the two electrodes of at least one pair of electrodes (E1, E2), a nominal electric field of more than 1 kV / mm, starting from a supply voltage lower than 50 V, preferably comprised between 1 V and 30 V, very preferably comprised between 3 V and 10 V.

4. A sensor arrangement according to any one of claims 1 to 3, wherein two electrodes of at least one pair of electrodes (E1, E2) are obtained as thin films, preferably having a thickness comprised between 50 nanometers and 2 micrometers, very preferably between 100 nanometers and 500 nanometers.

5. The circuit layout comprises at least the following: - A voltage source (V １ ), - at least one capacitor (C １ ), - controllable circuit means (SW), - Voltage source (V １ At least one capacitor (C １ ) connection and disconnection, at least one capacitor (C １ ) to and from at least two electrodes of a pair of electrodes (E1, E2); and a circuit means (SW) for - After the electric field is generated, or after the capacitor (C １ ) is the voltage source (V １ ) and connected to at least two electrodes of a pair of electrodes (E1, E2), and then at least one capacitor (C １ ) terminals of the representative voltage (V Ｃ ) measuring circuit means (V;OA ０ , O.A. １ , ADC MUX, ADC), The sensor device according to any one of claims 1 to 3, comprising:

6. The circuit layout comprises at least the following: - A voltage source (V １ ), - multiple reference resistors (R Ｒ ) a resistive voltage divider including - Voltage source (V １ a controllable circuit means (SW) for selectively connecting and disconnecting a reference resistor (R) between the first electrode (E1) and at least one of at least one pair of electrodes (E1, E2); - After the electric field is generated, or the voltage source (V １ After each reference resistor (R) is connected between the resistor divider and at least one of the at least one pair of electrodes (E1, E2), a representative voltage (V ＳＧ , V.R. Ｘ A measuring circuit means (V;OA) for measuring the value of ０ , ADC MUX, ADC), The sensor device according to any one of claims 1 to 3, comprising:

7. 4. The sensor device according to claim 1, wherein the circuit arrangement is configured to obtain a bipolar drive or to allow a reversal of the electrical polarity of two electrodes of at least one pair of electrodes (E1, E2) between two successive detection cycles.

8. The sensor arrangement according to any one of claims 1 to 3, wherein the at least one pair of electrodes (E1, E2) comprises a plurality of electrode pairs (E1, E2), each of which defines at least one sensing gap (G).

9. at least one electrode (E1) of the at least one pair of electrodes (E1, E2) has a peripheral profile with a generally pointed portion (E1a) which faces a corresponding portion (E2b) of the peripheral profile of the other electrode (E2) of the at least one pair of electrodes at a predetermined distance, or at least one electrode (E1) of the at least one pair of electrodes (E1, E2) has a peripheral profile with at least one axially extended portion (E1a) set at a predetermined distance between two extended parallel portions of the portion (E2b) of the peripheral profile of the other electrode (E2) of the at least one pair of electrodes, or A sensor device according to any one of claims 1 to 3, wherein two electrodes of at least one pair of electrodes (E1, E2) each have a peripheral profile with a substantially comb-shaped portion and are set in an interdigitated configuration at a predetermined distance from each other.

10. Temperature detector (RT １ ), and the circuit arrangement preferably further comprises a temperature detector (RT １ ) as a function of temperature detected by the Ｃ ;V ＳＧ ;V ＲＸ 4. The sensor device according to claim 1, configured to apply a calibration to measurements of

11. Sensing part (SG １ 4. The sensor device according to claim 1, wherein the at least one pair of electrodes (E1, E2) comprises at least one third electrode (E3) operatively associated with the at least one pair of electrodes (E1, E2), and the circuit arrangement is configured to use two electrodes of the at least one pair of electrodes (E1, E2) as source and drain electrodes, respectively, and the third electrode (E3) as a gate electrode, in particular for detecting the presence of a possible contaminant in the dielectric fluid (5).

12. Sensing part (SG １ ) is at least one of the following: - an electrically insulating support (31) for at least one pair of electrodes (E1, E2); - a silicon oxide substrate (31a) on a silicon wafer, on which at least one pair of electrodes (E1, E2) is provided, the silicon wafer preferably having a thickness not smaller than a given distance, particularly preferably a thickness greater than the given distance; - an electrically insulating support (31) supporting a third electrode (E3) operatively associated with at least one pair of electrodes (E1, E2), on which a layer of dielectric material (31c) is provided and on which at least one pair of electrodes (E1, E2) is provided; The sensor device according to any one of claims 1 to 3, comprising:

13. The sensor body is a sensing part (SG １ The at least one body portion (15) includes a sensing element (30) that supports the sensing element (30), and the at least one body portion (15) includes a dielectric body (5) that is disposed between the sensing element (SG) and the sensing element (SG). １ 2. The sensor device according to claim 1, further comprising one or more openings or passages (19, 19a) allowing contact with at least one pair of electrodes (E1, E2) of said first electrode (E1) and said second electrode (E2) of said second electrode (E1).

14. An annular sealing means (26) is provided between the wall (16a) of the at least one body part (15) and the detection element (30), the annular sealing means (26) together with the wall (16a) and the respective parts of the detection element (30) sealing the sensitive part (SG) carried by the detection element (30) into which one or more openings or passages (19) open. １ 14. The sensor apparatus of claim 13, defining a detection chamber facing said first electrode.

15. 1. An electrical device (1) having a casing (2) defining a storage stack (3) in which an electrical component (4) is arranged, the storage stack being suitable for receiving a dielectric fluid (5), the electrical device including a sensor device according to claim 1 for detecting the dielectric strength of the dielectric fluid (5).

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