Sensor

Abstract

Measuring device for measuring a measured quantity of a fluid, in particular a sensor such as a pressure sensor, relative pressure sensor, differential pressure sensor, displacement sensor or the like, comprising a housing (2), an elastic diaphragm (8) arranged in and / or on the housing (2), and a signal transmitter cooperating with the diaphragm (8), such that the action of the fluid on the diaphragm (8) causes a measurement signal at the signal transmitter corresponding to the measured quantity, characterized in that the diaphragm (8) comprises an electrically conductive, elastomeric layer (9), that the action of the fluid on the diaphragm (8) causes a change in the electrical capacitance of the diaphragm (8), and that the signal transmitter is formed by the diaphragm (8), in particular that the diaphragm (8) can be operated as a signal transmitter by providing the change in capacitance of the diaphragm (8) when the fluid acts upon it as a measurement signal.

Description

[0001] The invention relates to a measuring device according to the preamble of claim 1.

[0002] The measuring device can be a sensor, such as a pressure sensor, a relative pressure sensor, a differential pressure sensor, a displacement sensor, or the like. Such measuring devices are primarily used to measure a fluid's measurand. For example, the measuring device can be used to measure the water level in washing machines, dishwashers, wet and / or dry vacuum cleaners, or other household appliances. In particular, these measuring devices are pressure sensors for low pressures.

[0003] Such measuring devices are known, comprising a housing and an elastic membrane arranged in and / or on the housing. A signal generator interacts with the membrane, such that the action of the fluid on the membrane produces a measurement signal at the signal generator that corresponds to the measured variable. In the known measuring device, a magnet is used as the signal generator, which in turn interacts with a Hall sensor to generate the measurement signal. Both the magnet and the Hall sensor are cost-intensive components, making the measuring device unsuitable for use in cost-sensitive areas. Furthermore, it has been found that external influences on the measuring device can interfere with the signal generator, which in turn can distort the measurement signal.

[0004] The invention is based on the object of further developing the measuring device with a view to its cost-effectiveness. In particular, it is intended to create a stable measuring system that operates as independently of external influences as possible and in which the quality of the measurement signal is improved.

[0005] This object is achieved in a generic measuring device by the characterizing features of claim 1.

[0006] In the measuring device according to the invention, the membrane comprises an electrically conductive, elastomeric layer, wherein the action of the fluid on the membrane causes a change in the electrical capacitance of the membrane. Furthermore, the signal generator is formed by the membrane. Specifically, the membrane can be operated as a signal generator by providing the change in capacitance of the membrane upon exposure to the fluid as a measurement signal. In other words, the signal generator is integrated into the membrane, so that a magnet and a Hall sensor are not required. Due to the savings in components, a cost-effective measuring device is thus created. Further embodiments of the invention are the subject of the dependent claims.

[0007] In a further embodiment, which is characterized by high functional reliability, the membrane can comprise a first and a second electrically conductive layer. The two conductive layers can expediently be separated by an electrical insulation layer.

[0008] In a practical embodiment, the first electrically conductive layer and the second electrically conductive layer can be formed as electrodes on the electrical insulation layer. The electrodes can be arranged opposite one another on the respective surface of the insulation layer in a simple manner. Furthermore, the electrodes, with the insulation layer located between them, can form an electrical capacitor. This allows for particularly simple evaluation of the capacitance change for generating the measurement signal. Furthermore, a disproportionate change in capacitance occurs with a change in the fluid action on the membrane, thus allowing for a particularly sensitive measurement signal.

[0009] To apply an electrical voltage to the electrodes, the electrode can be electrically connected to an electrical connection. The electrical connection can be simply constructed by applying an electrically conductive layer to the surface of the insulating layer. For the sake of functional reliability and ease of contact, the electrical connection can also be arranged leading from the periphery of the insulating layer to the electrode.

[0010] A simple geometry for the arrangement can be achieved by designing the insulation layer essentially circular. The electrode, in turn, can be essentially circular with a smaller diameter than the insulation layer. The electrode can then expediently be arranged essentially concentrically with respect to the periphery of the insulation layer. Of course, a different geometry can also be chosen. For example, the electrodes and / or the insulation layer can also be rectangular, elliptical, diamond-shaped, or similar.

[0011] In a functionally reliable and cost-effective manner, the insulation layer can be made of an elastomer. The elastomer can be silicone, particularly a silicone film. The insulation layer can have a thickness in the range of approximately 0.05 mm to 0.2 mm. Preferably, the insulation layer has a thickness of approximately 0.1 mm.

[0012] The electrically conductive layer can also be made of an elastomer provided with electrically conductive particles in a functionally reliable and cost-effective manner. The elastomer can be made of silicone, and the electrically conductive particles can be made of graphite. In this case, the insulating layer and the electrically conductive layer are essentially made of the same materials, so that a largely stress-free deformation of the insulating layer and the electrically conductive layer occurs when exposed to the fluid. This advantageously counteracts the occurrence of cracks and / or detachments in the insulating layer and the electrically conductive layer. The electrically conductive layer can be printed, laminated, or similarly applied as an electrode to the surface of the insulating layer, thus ensuring its ease of manufacture.The thickness of the electrically conductive layer can preferably be a maximum of 0.1 mm. In particular, the thickness of the electrically conductive layer can be in the range of approximately 1 nm to 0.1 mm.

[0013] For ease of assembly, the membrane can be pre-tensioned and attached to a support. For ease of manufacture, the attachment can be achieved by gluing, welding, hot-staking, or similar means. It may be appropriate to attach the membrane to the support at the periphery of the insulation layer. If the housing is at least partially approximately cylindrical, it may also be appropriate for the support to be designed as a support ring. The support can be conveniently arranged in a pressure chamber within the housing.

[0014] To further counteract distortion of the measurement signal due to external influences, an additional electrically conductive elastomer layer can be provided, which serves as a reference for the measurement signal on the membrane. The additional electrically conductive elastomer layer can conveniently be arranged in the pressure chamber. Furthermore, the additional elastomer layer can be easily attached to the side of the carrier opposite the membrane.

[0015] For easy fluid supply, a connection port for supplying the fluid to the pressure chamber can be arranged on the housing. To ensure unobstructed access to the membrane for the fluid, an opening corresponding to the connection port can be located in the additional elastomer layer.

[0016] The following can be stated for a particularly preferred embodiment of the measuring device according to the invention.

[0017] Pressure sensors are used in various end devices to measure pressure. This pressure can be measured absolutely, relative (usually relative to ambient pressure), or differentially, which represents the pressure difference between two different pressures. This measured value is usually transmitted to a higher-level control and / or regulation electronics, which interprets and further processes the signal.

[0018] An example of such a device is a washing machine, where the water level is usually measured as a relative pressure to the ambient environment. To do this, the water pressure is measured at the bottom of the water tank. In this example, the pressure signal is used to monitor the water level and adjust the washing parameters accordingly.

[0019] The basic task is to convert the pressure to be measured into an electrical measurement signal. However, various environmental conditions have a negative impact on the sensor. These environmental conditions can include vibrations, humidity, temperature, various types of contamination, and the like. Furthermore, customers demand increasingly more precise, yet more cost-effective products. Therefore, the challenge here is to develop a cost-effective, robust, yet accurate pressure sensor.

[0020] Previous solutions are based on the Hall effect or inductive systems, which inherently require multiple components for measurement. For example, a moving magnet is required on the pressure side and a Hall element with output electronics on the electronics side. The inventive solution reduces the required components to an absolute minimum and integrates the sensor element as a capacitive structure directly into the membrane required for pressure sealing. The membrane is pre-tensioned using a carrier and can optionally be calibrated with a reference membrane. This type of capacitive measurement is proven and cost-effective.

[0021] The result is a pressure sensor with capacitive measuring technology that is structured directly onto a membrane for pressure measurement. The membrane is an elastomer with capacitive structures.

[0022] The advantages achieved by the invention are, in particular, that the measuring device according to the invention is particularly cost-effective. This allows the measuring device to be used with cost-sensitive devices. In particular, it can be used to open up applications that are not accessible with current technology. Furthermore, the measuring device is simpler and / or more easily scalable in its measuring range. This allows for easy adaptation of the measuring device with regard to cost, accuracy, etc.

[0023] An embodiment of the invention with various developments and refinements is shown in the drawings and is described in more detail below. Fig. 1 a pressure sensor with a membrane in exploded view, Fig. 2 a section through the membrane Fig. 1 in a first version, Fig. 3 a section through the membrane Fig. 1 in a second version, Fig. 4 the top view of the electrodes comprising membrane from Fig. 1 in a detailed view, Fig. 5 the arrangement of the electrodes Fig. 4 and Fig. 6 a principle representation of the effect of a fluid on the membrane according to a section as in Fig. 2.

[0024] In Fig. Figure 1 shows a pressure sensor serving as a measuring device 1 for measuring a fluid variable, specifically the pressure of a liquid in a household appliance. The pressure sensor 1 has a housing 2, on which a connection piece 3 for supplying the liquid to be measured is arranged, as well as a plug connection 4 for connecting the electrical supply lines. The pressure sensor 1 can be mounted in the household appliance by means of a locking mechanism 5 located on the housing 2. The housing 2 finally comprises a base 6 and a cover 7.

[0025] An elastic membrane 8 is arranged in and / or on the housing 2, onto which the liquid acts via the connecting piece 3. According to the pressure prevailing in the liquid, the membrane 8 is bent, as shown in a schematic diagram in Fig. 6. The membrane 8 comprises an electrically conductive, elastomeric layer 9 (see Fig. 2), so that the action of the fluid on the membrane 8 causes a change in the electrical capacitance of the membrane 8 due to its deflection. The membrane 8 can thus be operated as a signal transmitter in that the change in the electrical capacitance of the membrane 8 upon exposure to the fluid serves as a measurement signal, whereby the signal transmitter is formed by the membrane 8. Thus, in the present case, the signal transmitter interacting with the membrane 8, whereby the action of the fluid on the membrane 8 causes a measurement signal at the signal transmitter corresponding to the measured variable, is implemented as a single, integrated component.

[0026] As in Fig. As can be seen in Figure 2, in a further embodiment, the membrane 8 comprises a first electrically conductive layer 9 and a second electrically conductive layer 10. The two conductive layers 9, 10 are separated from each other by an electrical insulation layer 11. If the membrane 8 is subjected to an electrical voltage, the two layers 9, 10, which are spaced apart from each other due to the insulation layer 11, act as a capacitor. The capacitance of this capacitor formed by the layers 9, 10 is C=K⋅(A / d) where C is the capacitance, A is the surface of the membrane 8, d is the thickness of the membrane 8 and K is a constant. The constant includes the electric field constant of the vacuum ε0 and the relative permittivity ε r of the dielectric formed by the insulation layer 11. As can be seen from the Fig. As can be seen in Figure 6, due to the deflection of the membrane 8 under pressure, the surface area A' increases compared to the original surface A and, with it, the thickness d' decreases relative to the sum of the individual thicknesses d1+d2+d3 of the membrane 8. Consequently, the capacitance C increases disproportionately due to the pressure. As already mentioned, the respective existing capacitance or change in capacitance corresponds to the respective pressure of the fluid. The capacitance and pressure determination can be carried out using electronics (not shown), which are arranged, for example, in the housing 2.

[0027] The first electrically conductive layer 9 and the second electrically conductive layer 10 are expediently designed as electrodes 9', 10' on the electrical insulation layer 11. In Fig. 4 shows a plan view of the membrane 8 showing the electrode 9' located on the upper side of the insulation layer 11. The further electrode 10', not visible, is located on the underside of the insulation layer 11. The electrodes 9', 10' are arranged according to Fig. 5, in which the insulating layer 11 is omitted, are arranged opposite each other on the respective surface of the insulating layer 11. The electrodes 9', 10' with the insulating layer 11 located therebetween then form the electrical capacitor already described.

[0028] As in Fig. As can be seen in Figure 4, the electrode 9' is electrically connected to an electrical connection 18. The electrical connection 18 is arranged leading from the periphery 20 of the insulation layer 11 to the electrode 9' and serves to apply the electrical voltage to the electrode 9'. A similar electrical connection 19 leading from the periphery 20 of the insulation layer 11 establishes the electrical connection to the electrode 10', as can be seen from the Fig. 5. The electrical connection 18, 19 consists of an electrically conductive layer applied to the respective surface of the insulation layer 11. Based on the electrical voltage applied between the electrical connections 18, 19, the value of the electrical capacitance C of the capacitor formed by the membrane 8, caused by the action of the fluid on the membrane 8, can then be determined.

[0029] In a preferred embodiment, the insulation layer 11 is essentially circular, as shown in Fig. 4 and Fig. 5. The electrode 9', 10' is also essentially circular. However, the electrode 9', 10' has a smaller diameter relative to the insulation layer 11. Furthermore, the electrode 9', 10' is arranged essentially concentrically with respect to the periphery 20 of the insulation layer 11.

[0030] The insulation layer 11 consists of an elastomer. Silicone has proven to be a particularly suitable elastomer. In particular, the insulation layer 11 is a silicone film. The insulation layer 11 has a thickness d1 (see Fig. 6) in the range of approximately 0.05 to 0.2 millimeters. A thickness d1 of approximately 0.1 millimeters is preferred for the insulation layer 11. The electrically conductive layer 9, 10 consists of an elastomer provided with electrically conductive particles. Silicone as an elastomer and graphite as an electrically conductive particle have proven particularly suitable. The electrically conductive layer 9, 10 can be printed, laminated, or the like as an electrode 9', 10' onto the surface of the insulation layer 11. The thickness d2, d3 of the electrically conductive layer 9, 10 (see Fig. 6) ranges from approximately 1 nanometer to 0.1 millimeter. It has been found that the thickness d2, d3 should preferably be a maximum of 0.1 mm.

[0031] For the purpose of simple arrangement of the elastic membrane 8 in the housing 2, the membrane 8 is pre-tensioned and attached to a support 12, as in Fig. 2. The membrane 8 can be attached to the support 12 by gluing, welding, hot-staking or similar means. The support 12 together with the membrane 8 is then Fig. 1 is arranged in the housing 2. If the pressure chamber 13 is approximately cylindrical, the support 12 is preferably a support ring. The membrane 8 is then expediently attached to the periphery 20 of the insulation layer 11 on the support 12.

[0032] How to continue in Fig.As can be seen in Figure 3, a further electrically conductive, elastomeric layer 14 can be provided as a reference for the measurement signal applied to the membrane 8. The further elastomeric layer 14 is also located in the pressure chamber 13 and is designed essentially identically to the membrane 8. External influences act essentially in a similar manner on the membrane 8 and the further elastomeric layer 14, but the pressure effect from the fluid is only present at the membrane 8. Due to the reference provided by the further elastomeric layer 14, the measurement signal can be corrected with regard to the external influences.

[0033] The additional elastomer layer 14 is attached to the side of the support 12 opposite the diaphragm 8. To ensure unhindered supply of the fluid according to arrow 16 into the pressure chamber 13, an opening 15 is located in the additional elastomer layer 14, which corresponds to the connection piece 3. If the diaphragm 8 is arranged in the housing 2 such that the fluid is supplied from the other side according to arrow 17, the opening 15 in the additional elastomer layer 14 can be omitted.

[0034] The invention is not limited to the described and illustrated embodiments. Rather, it also encompasses all developments within the scope of the invention defined by the claims. Thus, such a measuring device can be used not only in the entire field of pressure sensor technology, preferably in the low-pressure segment, as a pressure sensor, relative pressure sensor, differential pressure sensor, or the like, but also as a other sensor, such as a level sensor, displacement sensor, or the like. Furthermore, the measuring device can be used not only for household appliances but also in other applications, for example, in laboratory and chemical process engineering. Reference symbol list: 1 measuring device / pressure sensor 2 housings 3 connecting pieces 4 plug connection 5 Locking 6 sockets (from case) 7 Cover (of housing) 8 Membran 9 (first) conductive layer 9' electrode 10 (second) conductive layer 10' electrode 11 Insulation layer 12 carriers 13 Pressure chamber 14 (further) elastomer layer 15 Opening (in elastomer layer) 16,17 Arrow (for fluid supply) 18,19 (electrical) connection (of electrode) 20 Periphery (from insulation layer)

Claims

[1] Measuring device for measuring a measured variable of a fluid, in particular a sensor, such as a pressure sensor, relative pressure sensor, differential pressure sensor, displacement sensor or the like, with a housing (2), with an elastic membrane (8) arranged in and / or on the housing (2), and with a signal transmitter cooperating with the membrane (8) in such a way that the action of the fluid on the membrane (8) causes a measuring signal at the signal transmitter corresponding to the measured variable, characterized by that the membrane (8) comprises an electrically conductive, elastomeric layer (9), that the action of the fluid on the membrane (8) causes a change in the electrical capacitance of the membrane (8), and that the signal generator is formed by the membrane (8), in particular that the membrane (8) can be operated as a signal generator in that the change in capacitance of the membrane (8) upon exposure to the fluid is provided as a measuring signal. [2] Measuring device according to claim 1, characterized bythat the membrane (8) comprises a first electrically conductive layer (9) and a second electrically conductive layer (10), wherein preferably the two conductive layers (9, 10) are separated by an electrical insulation layer (11). [3] Measuring device according to claim 1 or 2, characterized by that the first electrically conductive layer (9) and the second electrically conductive layer (10) are formed as electrodes (9', 10') on the electrical insulation layer (11), that the electrodes (9', 10') are preferably arranged opposite one another on the respective surface of the insulation layer (11), and that further preferably the electrodes (9', 10') form an electrical capacitor with the insulation layer (11) located therebetween. [4] Measuring device according to claim 1, 2 or 3, characterized bythat the electrode (9', 10') is electrically connected to an electrical connection (18, 19), that preferably the electrical connection (18, 19) consists of an electrically conductive layer applied to the surface of the insulation layer (11), and that further preferably the electrical connection (18, 19) is arranged leading from the periphery (20) of the insulation layer (11) to the electrode (9', 10'). [5] Measuring device according to one of claims 1 to 4, characterized by that the insulation layer (11) is substantially circular, that preferably the electrode (9', 10') is substantially circular with a smaller diameter than the insulation layer (11), and that further preferably the electrode (9', 10') is arranged substantially concentrically with respect to the periphery (20) of the insulation layer (11). [6] Measuring device according to one of claims 1 to 5, characterized bythat the insulation layer (11) consists of an elastomer, that the elastomer is preferably silicone, in particular a silicone film, and that further preferably the insulation layer (11) has a thickness in the range of approximately 0.05 to 0.2 mm, preferably of approximately 0.1 mm. [7] Measuring device according to one of claims 1 to 6, characterized by that the electrically conductive layer (9, 10) consists of an elastomer provided with electrically conductive particles, that the elastomer preferably consists of silicone, that further preferably the electrically conductive particles consist of graphite, that even more preferably the electrically conductive layer (9, 10) is printed, laminated or the like as an electrode (9', 10') onto the surface of the insulation layer (11), and that even more preferably the thickness of the electrically conductive layer is a maximum of 0.1 mm, in particular in the range from approximately 1 nm to 0.1 mm. [8] Measuring device according to one of claims 1 to 7, characterized by that the membrane (8) is fastened in a prestressed manner to a carrier (12), in particular by means of gluing, welding, hot caulking or the like, that the membrane (8) is preferably fastened to the periphery (20) of the insulation layer (11) on the carrier (12), in particular on a carrier ring, and that further preferably the carrier (12) is arranged in a pressure chamber (13) in the housing (2). [9] Measuring device according to one of claims 1 to 8, characterized by that a further electrically conductive, elastomeric layer (14) is provided as a reference for the measuring signal on the membrane (8), in particular in the pressure chamber (13), and that preferably the further elastomeric layer (14) is attached to the side of the carrier (12) opposite the membrane (8). [10] Measuring device according to one of claims 1 to 9, characterized bythat a connecting piece (3) for supplying the fluid into the pressure chamber (13) is arranged on the housing (2), and that preferably an opening (15) in the further elastomeric layer (14) corresponds to the connecting piece (3).

Images