SENSOR

Description

[0001] The invention relates to a measuring device according to the preamble of patent 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 similar. Such measuring devices are primarily used to measure a fluid's measurand.

[0003] For example, the measuring device can be used to measure water levels in washing machines, dishwashers, wet and / or dry vacuum cleaners, or other household appliances. These measuring devices are, in particular, pressure sensors for low pressures.

[0004] 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. The known measuring device uses a magnet 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.

[0005] Measuring devices and in particular aspects of pressure measuring devices are known in the prior art, for example from the documents WO 01 / 42776 A1, EP 2 876 421 A1, DE 10 2009 051176 A1 and in particular DE 10 2005 008959 A1.

[0006] 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.

[0007] This object is achieved in a generic pressure measuring device by the characterizing features of claim 1.

[0008] 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 transmitter is formed by the membrane. Specifically, the membrane can be operated as a signal transmitter by providing the change in capacitance of the membrane upon exposure to the fluid as a measurement signal. In other words, the signal transmitter is integrated into the membrane, so that a magnet and a Hall sensor are not required.

[0009] Due to the reduction in components, a cost-effective measuring device is thus created. Further embodiments of the invention are the subject of the dependent claims.

[0010] According to the invention, the membrane comprises a first and a second electrically conductive layer.

[0011] Furthermore, the two conductive layers are separated by an electrical insulation layer.

[0012] In addition, the first electrically conductive layer and the second electrically conductive layer are formed as electrodes on the electrical insulation layer. The electrodes are arranged opposite each other on the respective surfaces of the insulation layer in a simple manner. The electrodes, together with the insulation layer located between them, 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 resulting in a particularly sensitive measurement signal.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] For ease of installation, 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 methods. It may be advisable to fix the membrane to the

[0018] The periphery of the insulation layer is to be secured to the carrier. If the housing is at least partially approximately cylindrical, it may also be appropriate for the carrier to be designed as a carrier ring. The carrier can expediently be arranged in a pressure chamber within the housing.

[0019] 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.

[0020] To facilitate 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.

[0021] The following can be stated for a particularly preferred embodiment of the measuring device according to the invention.

[0022] Pressure sensors are used in various end devices to measure pressure. This pressure can be measured absolutely, relative (usually relative to ambient pressure), or differential (meaning pressure differences between two different pressures). This measured value is usually forwarded to higher-level control and / or regulation electronics, which interprets and further processes the signal. An example of such an end device is a washing machine, where the water level is usually measured as a pressure relative to the ambient pressure. For this purpose, 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.

[0023] 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.

[0024] Previous solutions are based on the Hall effect or inductive systems, which inherently require multiple components for measurement. For example, a moving magnet on the pressure side and a Hall element with output electronics on the electronics side are required. 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.

[0025] 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.

[0026] 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.

[0027] An embodiment of the invention with various developments and refinements is shown in the drawings and is described in more detail below. Fig. 1a pressure sensor with a membrane in exploded view, Fig. 2a section through the membrane from Fig. 1 in a first embodiment, Fig. 3 a section through the membrane of Fig. 1 in a second embodiment, Fig. 4 the top view of the electrodes comprising membrane made of Fig. 1 in a detailed view, Fig. 5 the arrangement of the electrodes from 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 .

[0028] In Fig. 1 1 shows a pressure sensor which serves as a measuring device 1 for measuring a measured variable of a fluid, in this case 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 on the housing 2. The housing 2 finally comprises a base 6 and a cover 7. An elastic membrane 8 is arranged in and / or on the housing 2, onto which the liquid acts via the connection piece 3. The membrane 8 is bent in accordance with the pressure prevailing in the liquid, 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.

[0029] As in Fig. 2 As can be seen, 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 area 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 ε 0 and the relative permittivity ε r of the dielectric formed by the insulation layer 11. As can be seen from the Fig. 6 As can be seen, 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 in relation 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 by means of electronics (not shown in detail), which are arranged, for example, in the housing 2.

[0030] The first electrically conductive layer 9 and the second electrically conductive layer 10 are expediently structured as electrodes 9', 10' on the electrical insulation layer 11. In Fig. 4 In a top view of the membrane 8, the electrode 9' located on the upper side of the insulation layer 11 can be seen. The additional 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.

[0031] As in Fig. 4 As can be seen, 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.

[0032] In a preferred embodiment, the insulation layer 11 is essentially circular, as shown in Fig. 4 und Fig. 5 can be seen. The electrode 9', 10' is also essentially circular in shape. However, the electrode 9', 10' has a smaller diameter in relation 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. 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 dl (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.

[0033] 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 can be seen. The membrane 8 can be attached to the support 12 by gluing, welding, hot-staking or similar methods. The support 12 together with the membrane 8 is then Fig. 1 The pressure chamber 13 shown in the figure 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 support 12 at the periphery 20 of the insulation layer 11.

[0034] How to continue in Fig. 3As can be seen, 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 the same way 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. The further elastomeric layer 14 is attached to the side of the carrier 12 opposite the membrane 8. In order to ensure unhindered supply of the fluid according to the arrow 16 into the pressure chamber 13, an opening 15 is located in the further elastomeric layer 14, which corresponds to the connection piece 3.If the membrane 8 is arranged in the housing 2 in such a way that the fluid is supplied from the other side according to the arrow 17, the opening 15 in the further elastomer layer 14 can be omitted.

[0035] 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 patent 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:

[0036] 1:Measuring device / pressure sensor 2:Housing 3:Connection piece 4:Plug connection 5:Locking mechanism 6:Base (of housing) 7:Cover (of housing) 8:Membrane 9:(First) conductive layer 10:(Second) conductive layer 10':Electrode 11:Insulation layer 12:Carrier 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 (of insulation layer)

Claims

1. A pressure measuring device for measuring the pressure of a fluid, having a housing (2), an elastic membrane (8) arranged within the housing (2) and / or on the housing (2), and a signal transducer cooperating with the membrane (8), wherein the signal transducer cooperates with the membrane (8) such that the action of the fluid on the membrane (8) causes a measuring signal corresponding to the measured variable at the signal transducer, and wherein the membrane (8) comprises an electrically conductive, elastomeric layer (9), the action of the fluid on the membrane (8) causes a change in the electric capacitance of the membrane (8), and the signal transducer is formed by the membrane (8) by the change in capacitance of the membrane (8) upon action of the fluid being provided as the measuring signal, characterized in that the membrane (8) comprises a first electrically conductive layer (9) and a second electrically conductive layer (10), wherein the two conductive layers (9, 10) are separated by an electrically insulating layer (11), wherein the first electrically conductive layer (9) and the second electrically conductive layer (10) are configured as electrodes (9', 10') on the electrically insulating layer (11), wherein the electrodes (9', 10') are arranged opposite to one another on the respective surface of the insulating layer (11), and wherein the electrodes (9', 10') form an electric capacitor with the insulating layer (11) located therebetween.

2. The pressure measuring device according to claim 1, characterized in that the electrode (9', 10') is electrically connected to an electrical terminal (18, 19).

3. The pressure measuring device according to the preceding claim, wherein the electrical terminal (18, 19) consists of an electrically conductive layer applied onto the surface of the insulating layer (11).

4. The pressure measuring device according to any one of the two preceding claims, wherein the electrical terminal (18, 19) is arranged leading from the periphery (20) of the insulating layer (11) to the electrode (9', 10').

5. The pressure measuring device according to any one of claims 1 to 4, characterized in that the insulating layer (11) is designed to be substantially circular.

6. The pressure measuring device according to the preceding claim, wherein the electrode (9', 10') is designed to be substantially circular having a smaller diameter relative to the insulating layer (11).

7. The pressure measuring device according to any one of the two preceding claims, wherein the electrode (9', 10') is arranged substantially concentrically relative to the periphery (20) of the insulating layer (11).

8. The pressure measuring device according to any one of claims 1 to 7, characterized in that the insulating layer (11) consists of an elastomer.

9. The pressure measuring device according to the preceding claims, wherein the elastomer is silicone, in particular a silicone film.

10. The pressure measuring device according to any one of the two preceding claims, wherein the insulating layer (11) has a thickness in the range of 0.05 to 0.2 mm, in particular of 0.1 mm.

11. The pressure measuring device according to any one of claims 1 to 10, characterized in that the electrically conductive layer (9, 10) consists of an elastomer provided with electrically conductive particles.

12. The pressure measuring device according to the preceding claim, wherein the elastomer consists of silicone, in particular wherein the electrically conductive particle consists of graphite, in particular wherein the electrically conductive layer (9, 10) is printed or laminated on the surface of the insulating layer (11) as an electrode (9', 10'), wherein the thickness of the electrically conductive layer is in particular no more than 0.1 mm and more particularly in the range of 1 nm to 0.1 mm.

13. The pressure measuring device according to any one of claims 1 to 12, characterized in that the membrane (8) is fixed to a support (12) in a biased manner, in particular by means of bonding, welding or staking, in particular, the membrane (8) is fixed to the periphery (20) of the insulating layer (11) at the support (12), in particular on a support ring, and more particularly, the support (12) is arranged in a pressure chamber (13) within the housing (2).

14. The pressure measuring device according to any one of claims 1 to 13, characterized in that a further electrically conductive, elastomeric layer (14) is provided on the membrane (8), in particular in the pressure chamber (13), as a reference for the measuring signal, and in particular, the further elastomeric layer (14) is fixed to the side of the support (12) opposite the membrane (8).

15. The pressure measuring device according to any one of claims 1 to 14, characterized in that a connecting piece (3) for supplying the fluid into the pressure chamber (13) is arranged on the housing (2), and in particular, an opening (15) in the further elastomeric layer (14) corresponds to the connecting piece (3).