Sensor

Abstract

Measuring device for measuring a measured quantity of a fluid, comprising a housing (3) and a diaphragm (4) arranged in and / or on the housing (3), wherein a signal transmitter (5) is in operative connection with the diaphragm (4), and wherein a signal receiver (6) magnetically interacts with the signal transmitter (5), wherein a shield (7) for external magnetic fields is arranged in the housing (3) such that the magnetic interaction of the signal receiver (6) and the signal transmitter (5) is unaffected by external magnetic fields, characterized in that the housing (3) consists of a plastic to which a soft magnetic component is added as a shield (7) in such a way that a soft magnetic shield is created to shield the external magnetic fields.

Description

The invention relates to a measuring device according to claim 1. The measuring device can be a sensor, such as an inductive sensor, a pressure sensor, a displacement sensor, or the like. Such measuring devices are primarily used for the direct measurement of operating parameters in a fluid. For example, these could be operating parameters in water-bearing parts of household appliances, such as washing machines or dishwashers. Measuring devices for measuring a fluid quantity are known, comprising a housing and a diaphragm arranged in and / or on the housing. A signal transmitter is operatively connected to the diaphragm. A signal transducer interacts magnetically with the signal transmitter to generate the measurement signal. It has been found that such magnetically or inductively operating measuring devices, particularly those based on Hall elements and magnets in the form of a displacement-to-voltage converter, have the disadvantage of being influenced by external magnetic fields, which in turn impairs their measurement accuracy. Furthermore, delays and / or hysteresis effects can occur during diaphragm movement, especially its return to its original position, which also impairs measurement accuracy. Such undesirable return effects can also occur with non-magnetically operating signal transmitters and transducers. Various other measuring devices and aspects of such measuring devices that constitute a relevant state of the art are also known, for example, from documents JP H03-115749A, DE 3640942A1, WO 2009 / 080603A1, GB 2256050A, JP H10-170377A, US 2008 / 0148807A1 and DE 102007018759A1. The invention is based on the objective of designing the measuring device in such a way that it is largely protected from impairment by external magnetic fields. This problem is solved by a measuring device as defined by the features of claim 1. In the measuring device according to the invention, a shield for external magnetic fields is arranged in and / or on the housing. This ensures that the magnetic interaction between the signal sensor and the signal transmitter remains essentially unaffected by external magnetic fields. The invention thus provides, for example, a pressure sensor with soft magnetic shielding. In a further embodiment of the measuring device according to the invention, the diaphragm and / or the signal transmitter is resettable by means of an elastic element designed in the form of a leaf spring. The reset of the diaphragm is thus essentially effected by the elastic element, thereby rendering any potential malfunctions caused by the diaphragm ineffective. Further embodiments of the invention are the subject of the dependent claims. In a simple and cost-effective design, the signal transmitter consists of a permanent magnet, and the signal receiver consists of a Hall sensor interacting with the permanent magnet. Advantageously, the permanent magnet is mounted in a magnetic adapter. The magnetic adapter, in turn, is operatively connected to the diaphragm, with a simpler, easier-to-mount design featuring a projection on the diaphragm that fits over an edge of the magnetic adapter. The elastic element acts on the magnet adapter to ensure the reliable return of the permanent magnet and / or the diaphragm. For compactness, the leaf-spring-like elastic element can be designed as a flat coil spring. The leaf spring can be manufactured cost-effectively as a stamped metal part. Manufacturing can be further simplified if the plastic magnet adapter is attached to the leaf spring by hot crimping. To ensure a good seal, the diaphragm, made of silicone for example, is fitted over the leaf spring. In a further, assembly-friendly embodiment, the housing consists of a housing body and a housing cover, the housing cover being essentially snapped into place on the housing body in a sealed manner. A fluid supply line to the diaphragm can be arranged on the housing, preferably on the housing cover. This supply line can further be arranged such that the fluid flows via the supply line to the projection on the diaphragm, which in turn interacts directly with the magnetic adapter to adjust the magnet. Such an embodiment is characterized by high operational reliability. Particularly effective elimination of magnetic interference fields is achieved by using a soft magnetic metal for the shielding, as described in the invention. The shielding largely lines the interior of the housing, which contains the signal receiver and transmitter. Mu-metal, for example, is a suitable material for the shielding. Furthermore, the housing consists of a plastic, for example a thermoplastic polymer, to which a soft magnetic component is added. To enable conventional injection molding of the housing components, the soft magnetic component can be added to the plastic material in the form of powder and / or fibers. Tests have shown that good shielding effects are achieved when the filler content of the soft magnetic component is greater than 20% of the plastic.The material for the soft magnetic component can be, for example, iron (Fe), iron-silicon (FeSi), carbonyl iron, ferrites or the like. In summary, the following can be stated for a preferred embodiment. Shielding of the sensor against external, interfering magnetic fields is achieved by adding a soft magnetic component, e.g., FeSi, to the polymer with a filler content greater than 20% in the form of powder or fibers. Advantageously, the existing injection molds for manufacturing the sensor housing can be used for this purpose. The advantages achieved with the invention consist in particular of a significant reduction in external magnetic interference affecting the measuring device. Furthermore, diaphragm reset inaccuracies can be largely avoided. This, in turn, advantageously leads to an increase in measurement accuracy. An embodiment of the invention with various further developments and configurations is shown in the drawings and is described in more detail below. Fig. 1 shows a pressure sensor in perspective view, Fig. 2 shows the pressure sensor cut along line 2-2 in Fig. 1 in perspective view, Fig. 3 shows a planar section along line 2-2 in Fig. 1, Fig. 4 shows an elastic element located in the pressure sensor as a single component in perspective view, and Fig. 5 shows a membrane located in the pressure sensor as a single component in perspective view. Figure 1 shows a measuring device 1, which is a pressure sensor for the washing liquid contained in the drum of a washing machine. To measure the pressure exerted by the fluid, it can be supplied to the pressure sensor 1 via a supply line 2. As can be seen further in Fig. 3, the pressure sensor 1 has a housing 3, in which a diaphragm 4 is arranged in and / or on the housing 3. A signal transmitter 5, which may be a permanent magnet, is operatively connected to the diaphragm 4. A signal transducer 6, which is in magnetic interaction with the signal transmitter 5 and may, for example, be a Hall sensor, is located in the housing 3. The signal transducer 6, which is arranged on a circuit board 17 inside the housing 16, generates a signal corresponding to the position of the signal transmitter 5, which is assumed according to the deflection of the diaphragm 4 due to the pressure prevailing in the washing liquid. The pressure prevailing in the washing liquid can then be determined from this signal. For this purpose, evaluation electronics (not shown), for example a microprocessor, may be located on the circuit board 17.The measured pressure and / or the signal generated by the sensor 6 is then available at a plug-in output 19 on the housing 3, where a connector 18 can be plugged in to transmit the signals to the circuit board 17. A shield 7 for external magnetic fields, which is explained in more detail below, is arranged in and / or on the housing 3, such that the magnetic interaction of the sensor 6 and the transmitter 5 is essentially unaffected by the external magnetic fields present in the washing machine. The permanent magnet 5 is mounted in a magnetic adapter 8, so that the pressure of the washing fluid acting on the diaphragm 4 simultaneously moves the magnetic adapter 8 along with the magnet 5. An elastic element 9 acts on the magnetic adapter 8 to return the permanent magnet 5 and / or the diaphragm 4 to its original position. The elastic element 9, shown as a separate component in Fig. 4, to which the magnetic adapter 8 is attached, is designed as a flat spiral spring, similar to a leaf spring. This allows the leaf spring 9 to be manufactured cost-effectively as a stamped metal part, for example, made of copper beryllium, spring steel, or the like, by incorporating corresponding spirally extending recesses 20 into the disc-shaped, round metal part. Furthermore, such a spiral spring 9 is very compact, which in turn benefits the overall compactness of the pressure sensor 1. The magnetic adapter 8 is made of plastic and is attached to the leaf spring 9, as can be seen in Fig. 2.The magnetic adapter 8 can be attached to the leaf spring 9 by hot-stitching the plastic. As already mentioned, the magnetic adapter 8 is operatively connected to the diaphragm 4. For this purpose, the diaphragm 4 has a projection 10, which is fitted over an edge 12 of the magnetic adapter 8 as shown in Fig. 2 or Fig. 3. The diaphragm 4, which is shown in more detail in Fig. 5, is made of an elastic material, for example, silicone or a thermoplastic elastomer. Furthermore, the diaphragm 4 is also fitted over the leaf spring 9, as can be seen in Fig. 2 or Fig. 3. The diaphragm 4 thus seals the housing interior 16 of the pressure sensor 1 against the washing fluid. The supply line 2 located on the housing 3 allows the washing fluid to reach the diaphragm 4. There, the washing fluid acts on the projection 10 on the diaphragm 4, specifically on a recessed pressure surface 11 on the projection 10, visible in Fig. 5. As shown in Fig. 3, the housing 3 consists of a housing body 13 and a housing cover 14. The housing cover 14, located in the area of ​​the diaphragm 4, is attached to the housing body 13 by means of snap-fit ​​connections 15, essentially creating a sealed connection. The supply line 2 is integrally integrated with the housing cover 14. In a first embodiment, which is not shown in detail, the shielding can consist of a soft magnetic metal, for example, mu-metal, and line the interior of the housing 16, in which the signal receiver 6 and the signal transmitter 5 are located. A second embodiment for the shielding 7, which is shown in more detail in Fig. 3, is preferred due to its simpler and more cost-effective manufacturing. In this embodiment, the housing 3 consists of a plastic, for example, a thermoplastic polymer, to which a soft magnetic component is added as shielding 7.Since the entire housing 3, i.e. both the housing body 13 and the housing cover 14, consists of plastic with a soft magnetic component 7, which is shown in dashed lines in Fig. 3, the interior of the housing 16 is largely completely shielded against the effects of external magnetic fields. The soft magnetic component 7 can be added to the plastic material in the form of powder and / or fibers. This allows the plastic material with the soft magnetic component 7 to be processed by injection molding like a conventional thermoplastic, enabling the housing body 13 and the housing cover 14 to be manufactured in the conventional manner. As demonstrated by corresponding experiments, a very good magnetic shielding effect is achieved when the fill level of the soft magnetic component 7 is at least 20% of the plastic content. The soft magnetic component 7 can be iron (Fe), iron-silicon (FeSi), carbonyl iron, ferrite, or the like. The invention is not limited to the described and illustrated embodiments. Rather, it also encompasses all technically advanced developments within the scope of the invention defined by the claims. For example, such a pressure sensor 1 can also be used in other household appliances, such as a dishwasher. Furthermore, such a pressure sensor 1 can be used not only for household appliances but also in other applications, for example, for measuring pressure and / or level as parameters of a fluid in laboratory and chemical process engineering. Finally, the measuring device according to the invention can also serve as a displacement sensor or the like. Reference symbol list 1 Measuring device / pressure sensor 2 Lead wire 3 Housing 4 Diaphragm 5 Signal transmitter / permanent magnet / magnet 6 Signal receiver 7 Shielding / soft magnetic component 8 Magnetic adapter 9 Elastic element / leaf spring / coil spring 10 Attachment (to diaphragm) 11 Pressure surface (to attachment) 12 Edge (of magnetic adapter) 13 Housing body 14 Housing cover 15 Snap connection 16 Housing interior 17 Circuit board 18 Connector 19 Connector output 20 Recess (in leaf spring)

Claims

Measuring device for measuring a measured quantity of a fluid, comprising a housing (3) and a diaphragm (4) arranged in and / or on the housing (3), wherein a signal transmitter (5) is in operative connection with the diaphragm (4), and wherein a signal receiver (6) magnetically interacts with the signal transmitter (5), wherein a shield (7) for external magnetic fields is arranged in the housing (3) such that the magnetic interaction of the signal receiver (6) and the signal transmitter (5) is unaffected by external magnetic fields, characterized in that the housing (3) consists of a plastic to which a soft magnetic component is added as a shield (7) in such a way that a soft magnetic shield is created to shield the external magnetic fields. Measuring device according to the preceding claim, wherein the membrane (4) and / or the signal transmitter (5) is resettable by means of an elastic element (9) designed in the manner of a leaf spring. Measuring device according to claim 1 or 2, characterized in that the signal transmitter (5) consists of a permanent magnet. Measuring device according to the preceding claim, wherein the permanent magnet (5) is attached in a magnetic adapter (8), wherein the magnetic adapter (8) is in operative contact with the membrane (4) by means of a projection (10) on the membrane (4) being slipped over an edge (12) of the magnetic adapter (8). Measuring device according to claims 2 to 4, wherein the elastic element (9) acts on the magnet adapter (8) to reset the permanent magnet (5) and / or the diaphragm (4), and wherein the leaf spring-like elastic element (9) is designed as a flat spiral spring. Measuring device according to the preceding claim, wherein the plastic magnetic adapter (8) is attached to the leaf spring (9). Measuring device according to the preceding claim, wherein the diaphragm (4) is placed on the leaf spring (9). Measuring device according to one of the preceding claims 4 to 7, wherein a supply line (2) for the fluid to the membrane (4) is arranged on the housing (3), which is designed such that the fluid acts on the projection (10) on the membrane (4) via the supply line (2). Measuring device according to one of the preceding claims, wherein the soft magnetic component (7) is added to the plastic material in the form of powder and / or fibers. Measuring device according to the preceding claim, wherein the fill level of the soft magnetic component (7) is greater than 20% of the plastic content.

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