Capacitive level switch

Abstract

Capacitive level switch comprising a housing (12) which defines a main extension direction, a circuit board (1) arranged in the housing (12) with an active surface (5,6), wherein the level switch has a sensing area (2) which extends only transversely to the main extension direction, and wherein on one side, two active surfaces (5,6) are spaced apart from each other transversely to the main extension direction within a dumbbell-shaped counter electrode (9).

Description

Field of invention

[0001] The invention relates to a capacitive level switch which can be used as a level limit switch for liquids and bulk materials. Background of the invention

[0002] Vibration probes, also known as "vibrating fork sensors", are well-known in practice.

[0003] Vibration probes operate according to a simple physical measurement principle, whereby the resonance frequency of the vibrating fork is reduced when immersed in the medium to be measured.

[0004] Vibration probes have the advantage of being able to be installed in any position and that reliable measurement is possible regardless of the medium.

[0005] A disadvantage of vibrating probes is that they must not touch adjacent components and should always maintain a certain minimum distance from adjacent components to prevent the medium to be measured from becoming trapped in the space between the probe and the adjacent component.

[0006] Capacitive sensors, which can also be used as level switches, are also well-known in practice.

[0007] If a capacitive sensor is used solely as a level switch, it can be a disadvantage, depending on the application, that the switching distance depends, among other things, on the medium being detected. This necessitates that such a sensor be taught in using a teach-in procedure or adjusted using a potentiometer.

[0008] Typically, a capacitive sensor measures forward from an active surface, but also in all directions.

[0009] Patent application US 2009 / 0301189 A1 discloses a capacitive sensor arrangement for measuring the fill level of liquid material in a container, comprising an electronic component for receiving and processing signals and an antenna probe connected thereto. The antenna probe has an electrical conductor connected to the electronic component and an insulating layer at least partially covering the electrical conductor. An enlarged measuring section connected to the electrical conductor has a surface area larger than the surface area of ​​the electrical conductor over the corresponding height or length and serves as the first plate of the capacitive sensor arrangement, with the liquid material to be measured serving as the second plate.

[0010] Document US 2009 / 0139325 A1 relates to a sensor with electrodes on the inner layer of a multilayer printed circuit board (PCB) and with a measuring circuit. The PCB can consist of a first and a second layer, with the electrodes located between the layers. The electrodes can be located on the inner layer and the sensor circuit on the opposite outer layer. The components for the sensor circuit can be mounted on the PCB, so that the PCB and the components form a multilayer PCB assembly.

[0011] German patent application DE 10 2009 013 835 A1 describes a sensor plate for measuring the fill level of a storage container. The plate comprises a dielectric substrate with three electrodes arranged on its front surface. The electrode arrangement is a mirror image of a central plane, which, under operating conditions, is at the level of the monitored fill level. By comparing the capacitances of the two capacitors formed by the three electrodes, it is possible to monitor whether the minimum permissible fill level in the storage container has been reached or fallen below.

[0012] Document US 2006 / 0005622 A1 relates to a sensor system for measuring the fluid level in a bilge. First and second field-effect sensors are encapsulated or sealed in a container or in the bilge wall, vertically oriented, and each comprises a planar pattern of electrodes or conductive traces arranged on a printed circuit board along with integrated circuits. When the bilge fluid rises near the field-effect sensors, a change in the arc-shaped electric field is detected, and a bilge pump is automatically activated to pump fluid out of the bilge.

[0013] The publication DE 87 06 280 U1 discloses a capacitive, flexible sensor with three electrodes leading into an evaluation electronics, wherein the base plate is made of a flexible material.

[0014] German patent application DE 10 329 138 A1 (Rechner Industrie-Elektronik GmbH) proposes an electrode configuration for a capacitive sensor in which a grounded electrode assembly behind the active surface directs the detection area forward. This allows even distant objects to be detected.

[0015] When used simply as a level switch, a large switching distance is usually not desirable. On the contrary, it is often more advantageous to provide a sensor that reliably switches only when the medium is in close proximity or even touching the sensor housing.

[0016] Furthermore, in many cases it is desirable to provide a sensor that can be installed inside a pipe. This is problematic with the vibration sensors described above due to the small distance to the pipe wall.

[0017] Although capacitive sensors can be installed in a pipe, they only detect in the direction of a pipe opening with a larger switching distance, which is not desirable in many cases. Object of the invention

[0018] In contrast, the invention is based on the objective of providing a capacitive level switch which switches reliably and independently of the medium to be detected when it is in the immediate vicinity of the sensor.

[0019] A further objective of the invention is to provide a capacitive proximity switch which can be mounted in any installation position and is still reliably suitable as a level switch. Summary of the invention

[0020] The object of the invention is already solved by a capacitive level switch according to claim 1.

[0021] Preferred embodiments and further developments of the invention can be found in the subject matter of the dependent claims.

[0022] The invention relates to a capacitive level switch, i.e. a sensor which generates a switching signal according to the capacitive principle as soon as a bulk material or liquid to be detected has reached a maximum fill level.

[0023] The capacitive level switch comprises a housing that defines a main direction of extension. A circuit board is arranged within the housing in this main direction of extension; in particular, it is inserted into the housing.

[0024] The circuit board includes an active area or is connected to one. An active area is understood to be, in particular, a film made of conductive material, which acts as an excitation electrode for capacitive measurement.

[0025] According to the invention, the detection range of the level switch extends only transversely, in particular perpendicularly to the main direction of extension.

[0026] With regard to the circuit board, the level sensor only detects laterally, which makes it possible to provide a small laterally directed detection area, which only leads to the sensor being switched on when the medium to be measured is in the immediate vicinity of the sensor.

[0027] It is specifically intended that the maximum switching distance, regardless of the medium to be detected, is less than 15 mm, preferably less than 10 mm and particularly preferably less than 5 mm.

[0028] In particular, it is planned to provide the level switch with a housing which, at least in sections, has a shape that deviates from a circular cylindrical shape and has a minimum and a maximum radius.

[0029] The shape can be arbitrary. It is understood that for a non-circular cylindrical shape, starting from a center point, there is a maximum and a minimum extent.

[0030] The level switch is now designed so that the switching distance is smaller than the maximum radius of the housing, regardless of the medium.

[0031] For example, the housing can be inserted into a pipe and includes a housing component that deviates from a circular cylindrical shape, resulting in a cavity between the pipe wall and the non-circular cylindrical housing component.

[0032] Since the switching distance is now smaller than the maximum radius of the housing, the sensor does not switch based on the pipe wall thickness of the pipe in which it is installed. Rather, the sensor only switches when liquid rises into the pipe.

[0033] Preferably, the housing is essentially plate- or cuboid-shaped, at least in the area of ​​the active surface.

[0034] The cuboid shape can serve two purposes: firstly, to accommodate the circuit board; secondly, it has been found that a plate-shaped design increases resistance to adhering media.

[0035] At the same time, the sensor is preferably designed to be at least partially cylindrical. This allows the sensor to be easily inserted into a pipe or attached using a clamp.

[0036] In a preferred embodiment of the invention, an active area is arranged on both the front and back of the circuit board; in particular, the front and back have identically designed sensor areas, as will be described in detail below.

[0037] This design has the advantage that detection is possible all around the sensor. Thus, the switching distance does not change when the sensor is rotated around its own axis.

[0038] In a preferred embodiment of the invention, the active area and evaluation electronics are arranged on exactly one circuit board.

[0039] It is therefore a single-board sensor in which all essential components, including the sensor components, are arranged on a single circuit board.

[0040] This type of design is particularly robust and allows for easy manufacturing, as no sensor surfaces need to be wired to the circuit board.

[0041] In a preferred embodiment of the invention, a grounded surface is arranged in front of and / or behind the active surface with respect to the main direction of extension. In particular, an electrically conductive surface grounded is arranged on both sides with respect to the main direction of extension.

[0042] This ensures that the sensor is essentially only effective in the radial direction within the area of ​​the active surface, and not effective in the axial direction, i.e., in the direction of the main extension.

[0043] In general, the sensor components include at least one active surface, which shapes the field in the detection area.

[0044] Furthermore, there is at least one counter electrode, which is often also referred to as a measuring electrode. The sensor according to the invention preferably includes such a measuring electrode.

[0045] Furthermore, preferably a grounded surface, i.e. a ground electrode, is provided, via which the extent of the detection area can be determined.

[0046] The general wiring of such a sensor comprising three electrodes is known, in particular from DE 10 329 138 A1.

[0047] Preferably, unlike most sensors known from the prior art, the surfaces lie on a plane, in particular on a circuit board.

[0048] The level sensor comprises opposing active surfaces arranged perpendicular to the main direction of extension on one side.

[0049] Between these active surfaces, a surface lying on mass can again be arranged.

[0050] This centrally located mass interrupts the detection area, so that, particularly in the case of a plate-shaped housing section, the bulk material collecting in the center of the plate may not trigger the sensor.

[0051] The counter electrode is dumbbell-shaped, with an active area located between each individual dumbbell.

[0052] The area connecting the dumbbells thus runs between the active surfaces and preferably has a recess in which the aforementioned surface, which lies on mass, is arranged. Description of the drawings

[0053] The subject matter of the invention will below be described with reference to a schematically illustrated embodiment based on the drawings. Fig. 1 and Fig. 2 will be explained in more detail.

[0054] Referring to Fig. 1 First, the components of a circuit board 1, as used for a level switch according to the invention, will be explained in more detail.

[0055] The circuit board 1 has a length 1 and a width b.

[0056] Length 1 defines the main extension direction of board 1.

[0057] Circuit board 1 can be roughly divided into three sections: A detection area 2 with the sensor surfaces, an area 3 with evaluation electronics and a connection area 4, which is directly adjacent to area 3 with evaluation electronics.

[0058] It is therefore a single-board solution in which all components are arranged on a single board 1.

[0059] Detection area 2, which is the foremost area of ​​circuit board 1, is slightly narrower than the rest of the circuit board. The resulting step can serve as a stop when inserting it into a housing.

[0060] The detection area 2 comprises two opposing active areas 5, 6.

[0061] The detection area 2 is limited by the surfaces 7 and 8 lying on the mass.

[0062] Therefore, the sensor does not effectively detect anything outside the detection range 2 in the axial direction.

[0063] The counter electrode 9, which is also located between the electrically conductive surfaces 7 and 8 that are on ground, is dumbbell-shaped.

[0064] The two "dumbbells" extend across the width of the circuit board in the detection area approximately the same distance as the active areas 5 and 6.

[0065] The bridge connecting the two dumbbells, which runs between the active surfaces 5 and 6, includes a recess 10, within which another electrically conductive surface 11 lying on ground is arranged.

[0066] The surface 11 lying on the mass interrupts the detection area in the middle, so that it initially extends only in the area of ​​the bridge of the barbell up to the active surfaces 5 and 6.

[0067] Since an identical arrangement of sensor surfaces is applied to the back of the circuit board (not shown), the detection area extends radially around the circuit board.

[0068] The arrangement of sensor surfaces shown here made it possible to provide a detection area that extends only in a small area around the circuit board.

[0069] This results in the switching distance of the level switch being rather small and not directed forwards.

[0070] The level switch operates independently of the medium to be detected and can be operated in different installation positions.

[0071] The level switch only triggers a switching signal when the medium to be detected touches the housing or is in its immediate vicinity.

[0072] Fig. Figure 2 shows a schematic view of a housing 12. The housing 12 comprises a cylindrical section 13, a transition area 14 which is designed as a thread for screwing in the sensor and a plate-shaped section 15.

[0073] The in Fig. The circuit board shown can now be pushed into the cuboid section with the detection area leading.

[0074] The cylindrical section can also serve to mount the sensor. In this embodiment, the cylindrical area is flattened at the top of the casing to allow the attachment of a handling tool, such as a wrench.

[0075] The cylindrical section results in a maximum housing radius R max defined.

[0076] The sensor is designed in such a way that materials located in front of the sensor are not detected, and that the switching distance, relative to the sensor areas of the circuit board, is smaller than R. max This allows the sensor to be completely installed inside a pipe without the pipe wall being within the detection range.

[0077] The sensor according to the invention does not require a teach-in process; however, it is also conceivable to provide embodiments that can be put into a learning mode. Adjusting the sensor using a potentiometer is also conceivable.

[0078] The invention made it possible to provide a reliable level switch operating on the capacitive principle, which is particularly suitable as an alternative to a tuning fork sensor.

Claims

[1] Capacitive level switch comprising a housing (12) which defines a main extension direction, a circuit board (1) arranged in the housing (12) with an active surface (5,6), wherein the level switch has a sensing area (2) which extends only transversely to the main extension direction, and wherein on one side, two active surfaces (5,6) are spaced apart from each other transversely to the main extension direction within a dumbbell-shaped counter electrode (9). [2] Capacitive level switch according to the preceding claim, characterized by , that the housing (12) has at least a section-wise shape deviating from a circular cylindrical shape with a minimum and a maximum radius (r) max ) exhibits, wherein the switching distance of the level switch is smaller than the maximum radius, regardless of the respective medium. [3] Capacitive level switch according to the preceding claim, characterized by, that the housing (12) in the area of ​​the active surfaces (5,6) is essentially plate- or cuboid-shaped. [4] Capacitive level switch according to the preceding claim, characterized by , that the housing (12) is sectionally circular-cylindrical. [5] Capacitive level switch according to any one of the preceding claims, characterized by , that an active area (5,6) is arranged on the front and back of the circuit board (1), in particular that the front and back have identically designed sensor areas. [6] Capacitive level switch according to any one of the preceding claims, characterized by , that active areas (5,6) and evaluation electronics are arranged on exactly one circuit board. [7] Capacitive level switch according to any one of the preceding claims, characterized by , that with respect to the main extension direction in front of and / or behind the active surfaces (5,6) a surface lying on mass is arranged. [8] Capacitive level switch according to the preceding claim, characterized by , that a surface lying on mass (11) is arranged between the active surfaces (5,6). [9] Capacitive level switch according to the preceding claim, characterized by , that the dumbbell-shaped counter electrode (9) is centrally recessed in the area which extends between the active surfaces (5,6) along the main direction of extension, wherein a grounded surface (11) is arranged in the recessed area (10). [10] Capacitive level switch according to any one of the preceding claims, characterized by , that the housing (12) is inserted into a tube.

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