Method for producing an inductive conductivity sensor and inductive conductivity sensor

Abstract

The invention relates to an inductive conductivity sensor (100) comprising: - an electronic unit (10) comprising a circuit board (20), a transmitting coil (30), a receiving coil (40) and a temperature sensor (50), wherein the circuit board (20) extends along a first axis (Z) and has a first axial end (21) and a second axial end (22), wherein the printed circuit board (20) has a first plate side (23) and a second plate side (24), a first through-opening (25) and a second through-opening (26), wherein the first through-opening (25) is arranged between the first axial end (21) and the second axial end (22) of the printed circuit board (20) and the second through-opening (26) is arranged between the first axial end (21) and the first through-opening (25), so that a bracket (27) is formed between the first axial end (21) and the second through-opening (26), wherein the temperature sensor (50) is arranged on the bracket (27), wherein the transmitting coil (30) is arranged on the first plate side (23) around the first through-opening (25) and the receiving coil (40) is arranged on the second plate side (24) around the first through-opening (25), - a housing (60) which encloses the electronic unit (10) in a fluid-tight manner, so that the first through-opening (25) and the second through-opening (26) can each be at least partially flowed through by a fluid.

Description

The invention relates to a method for producing an inductive conductivity sensor and to an inductive conductivity sensor.Inductive conductivity sensors serve in a large number of applications in the laboratory and in process measurement technology for detecting the conductivity of a liquid measurement medium. They are preferably used where large measurement ranges and high chemical or thermal loads occur. This is the case, for example, in a large number of industrial chemical processes, but also in superheated steam sterilization processes, which are frequently used in the field of food technology because of the high hygiene requirements.An inductive conductivity sensor comprises a transmitting coil and a receiving coil, which are generally configured as ring coils, also referred to as toroidal coils. Such a conductivity sensor functions in the manner of a double transformer, wherein the transmitting and receiving coils are inserted into the measurement medium to such an extent that a closed current path running through the measurement medium and traversing the transmitting and receiving coils can form. When the transmitting coil is excited with an alternating voltage signal, it generates a magnetic field which induces a current in the self-contained medium path passing through the coils, the strength of said current depending on the electrical conductivity of the measurement medium. Since this alternating electric current in the medium in turn causes a varying magnetic field surrounding it, an alternating current is induced in the receiver coil. This alternating current supplied as an output signal by the receiver coil or a corresponding alternating voltage is a measure of the electrical conductivity of the measurement medium.Since the electrical conductivity of a measuring medium depends on the temperature of the measuring medium, it is of extreme importance to measure the temperature with the highest precision simultaneously and as far as possible also at the same location as the location where the conductivity measurement takes place.It is therefore an object of the invention to specify an inductive conductivity sensor and a method for producing the same, which sensor has a reliable, stable and simple temperature sensor.This object is achieved according to the invention by an inductive conductivity sensor according to claim 1 and by a production method according to claim 6.The inductive conductivity sensor according to the invention comprises:an electronics unit comprising a printed circuit board, a transmitting coil, a receiving coil and a temperature sensor, wherein the printed circuit board extends along a first axis and has a first axial end and a second axial end, wherein the printed circuit board has a first board side and a second board side, a first through-opening and a second through-opening, wherein the first through-opening is arranged between the first axial end and the second axial end of the printed circuit board and the second through-opening is arranged between the first axial end and the first through-opening, such that a bracket is formed between the first axial end and the second through-opening, wherein the temperature sensor is arranged on the bracket, wherein the transmitting coil is arranged on the first board side around the first through-opening and the receiving coil is arranged on the second board side around the first through-opening, and wherein,a housing which encloses the electronics unit in a fluid-tight manner, so that a fluid can flow through the first through opening and the second through opening in each case at least partially.The inductive conductivity sensor according to the invention makes it possible for the fluid to be measured to flow optimally against its temperature sensor, which leads to an optimum temperature sensitivity. Furthermore, the bracket shape achieves maximum stability and maximum robustness against mechanical action from the outside. Thanks to the connected configuration of the housing with the electronics unit, it is also achieved that minimum housing thicknesses are made possible for optimum sensitivity for the conductivity measurement and for the temperature measurement. Furthermore, the symmetrical arrangement of the temperature sensor makes it possible for the electromagnetic fields of the transmitting coil and receiving coil to be minimally influenced.According to one embodiment of the invention, the housing is integrally connected to the electronics unit by an injection molding method.According to one embodiment of the invention, the housing has a housing thickness and the housing thickness is less than 2 mm, preferably less than 1 mm, at least above the temperature sensor.According to one embodiment of the invention, the transmitting coil has a transmitting coil inner diameter, the receiving coil has a receiving coil inner diameter and the first through-opening has a first through-opening inner diameter, wherein the transmitting coil inner diameter and the receiving coil inner diameter are larger than the first through-opening inner diameter.According to an embodiment of the invention, the first through opening has a first through opening inner diameter and the second through opening has a second through inner diameter, wherein the second through inner diameter is equal to the first through opening inner diameter or greater than the first through opening inner diameter.The above object is also achieved by a method for manufacturing an inductive conductivity sensor according to claim 6.The method according to the invention comprises:providing an electronic unit and an injection mold, wherein the electronic unit comprises a printed circuit board, a transmitting coil, a receiving coil and a temperature sensor, wherein the printed circuit board extends along a first axis and has a first axial end and a second axial end, wherein the printed circuit board comprises a first board side and a second board side, a first through-opening and a second through-opening, wherein the first through-opening is arranged between the first axial end and the second axial end of the printed circuit board and the second through-opening is arranged between the first axial end and the first through-opening, such that a bracket is formed between the first axial end and the second through-opening, wherein the temperature sensor is arranged on the bracket, wherein the transmitting coil is arranged on the first board side and the receiving coil is arranged on the second board side in each case around the first through-opening, wherein,fixing the electronics unit relative to the injection mold with the aid of a clamping unit, the clamping unit clamping the circuit board at a clamping point,injecting a plastic material to form a housing of the inductive conductivity sensor,removing the clamping unit,closing the housing at the clamping point.According to an embodiment of the invention, the clamping unit clamps the circuit board at the first through-opening.According to one embodiment of the invention, the transmitting coil has a transmitting coil inner diameter, the receiving coil has a receiving coil inner diameter and the first through-opening has a first through-opening inner diameter, wherein the transmitting coil inner diameter and the receiving coil inner diameter are larger than the first through-opening inner diameter, so that a first annular surface is formed on the first plate side and a second annular surface is formed on the second plate side, wherein the clamping unit clamps the printed circuit board to the first annular surface and the second annular surface.According to one embodiment of the invention, the electronics unit has a first half shell and a second half shell, which are arranged in such a way that the transmitting coil and the receiving coil are protected, and the clamping unit clamps the printed circuit board onto the first half shell and the second half shell when the electronics unit is fixed.According to one embodiment of the invention, a welding mandrel and a welding cap are used when closing the housing at the clamping point, wherein the welding mandrel and the welding cap are welded to the housing by means of an ultrasonic method.The invention is explained in more detail with reference to the following description of the figures. The following are shown:FIG. 1 shows an exemplary illustration of an inductive conductivity sensor according to the invention,FIG. 2 is a sectional view of the inductive conductivity sensor shown in FIG. 1,FIG. 3 shows an exemplary illustration of the production of the inductive conductivity sensor shown in FIG. 1,FIG. 4 shows an enlarged detail of the inductive conductivity sensor shown in FIG. 2.The inductive conductivity sensor 100 according to the invention shown in FIGS. 1 to 4 comprises an electronics unit 10 and a housing 60.The electronic unit 10 comprises a printed circuit board 20, a transmitting coil 30, a receiving coil 40 and a temperature sensor 50 (see FIG. 2 ). The electronics unit 10 preferably further comprises a first half shell H 1 and a second half shell H 2, which in particular surround temperature- and / or pressure-sensitive components (see FIG. 4 ). The first half-shell H1 and the second half-shell H2, when placed one on top of the other, preferably have a substantially toroidal shape. It is thus achieved that the transmitting coil 30 and the receiving coil 40 are ideally protected by the two half shells H 1, H 2.The circuit board 20 extends along a first axis Z (see FIG. 3 ) and has a first axial end 21 and a second axial end 22.The circuit board 20 has a first board side 23 and a second board side 24, a first through-opening 25 and a second through-opening 26.The first through-opening 25 is arranged between the first axial end 21 and the second axial end 22 of the printed circuit board and the second through-opening 26 is arranged between the first axial end 21 and the first through-opening 25, so that a bracket 27 is formed between the first axial end 21 and the second through-opening 26. The bracket 27 is preferably formed symmetrically to the first axis Z. Preferably, the yoke 27 has the same outer radius as the transmitting coil 30 and the receiving coil 40 (see FIG. 1 ).The temperature sensor 50 is arranged on the bracket 27. The temperature sensor 50 is preferably arranged centrally on the bracket 27, that is to say along the first axis Z. This enables a symmetrical arrangement of the temperature sensor 50 on the inductive conductivity sensor 100. In FIG. 1, the temperature sensor 50 is covered by the housing 60, for which reason the temperature sensor 50 is illustrated in dashed lines.The transmitting coil 30 is arranged on the first plate side 23 around the first through-opening 25 and the receiving coil 40 is arranged on the second plate side 24 around the first through-opening 25.The housing 60 encloses the electronics unit 10 in a fluid-tight manner, so that a fluid can flow through the first through-opening 25 and the second through-opening 26, respectively. The housing 60 is integrally connected to the electronic unit 10 by an injection molding method. For protection against electromagnetic interference fields, the electronics unit 10 preferably has at least partially shield elements (not shown). The housing 60 has a housing thickness GDand the housing thickness GDis less than 2 mm, preferably less than 1 mm, at least above the temperature sensor 50.The transmitting coil 30 has a transmitting coil inner diameter SI, the receiving coil 40 has a receiving coil inner diameter EI, and the first through-opening 25 has a first through-opening inner diameter DI 1. According to one embodiment of the invention, the transmission coil inner diameter SI and the reception coil inner diameter EI are preferably larger than the first passage opening inner diameter DI 1. This implies that a first ring surface RF 1 is formed on the first plate side 23 and a second ring surface RF 2 is formed on the second plate side 24.The first through hole 25 has a first through hole inner diameter DI 1 and the second through hole 26 has a second through hole inner diameter DI 2.According to the embodiment illustrated in FIG. 1, the second passage inner diameter DI 2 is equal to or larger than the first passage opening inner diameter DI 1.Next, the method of manufacturing the above-described inductive conductivity sensor 100 according to the present invention will be described.First, the above-described electronic unit 10 and an injection mold (not shown) are provided. According to an advantageous step, the first half shell and the second half shell H 1, H 2 are then welded to one another by means of ultrasound. This enables, in particular, the printed circuit board 20 to be fixed and the transmitting coil 30 and the receiving coil 40 to be protected from injection pressure. Naturally, the injection mold has a mold surface which corresponds to the shape of the housing 60 of the inductive conductivity sensor 100 and makes it possible to accommodate the electronics unit 10. In the region of the first through-opening 25, the injection mold has a cutout which is complementary to a clamping unit 200.The electronics unit 10 is then fixed relative to the injection mold with the aid of the clamping unit 200 (see FIG. 3 ). The clamping unit 200 comprises, for example, a first tool core 201 and a second tool core 202. The clamping unit 200 clamps the printed circuit board 20 and / or preferably the two half shells H 1, H 2 at a clamping point. Preferably, the clamping unit 200 clamps the circuit board 20 at the first through hole 25.In the case where the transmission coil inner diameter SI and the reception coil inner diameter EI are larger than the first through hole inner diameter DI 1 so that a first ring surface RF 1 is formed on the first board side 23 and a second ring surface RF 2 is formed on the second board side 24, the clamping unit 200 preferably clamps the circuit board 20 to the first ring surface RF 1 and the second ring surface RF 2 (see FIG. 4 ).Next, injection of a resin material is performed to form the inductive conductivity sensor housing 60. The plastic material is preferably PEEK. The injection into the injection mold is preferably effected in the region of a flange of the housing 60. The clamping unit 200 seals the injection mold tightly in the region of the cutout of the injection mold.The clamping unit 200 is then removed. In this case, the first tool core 201 and the second tool core 202 are preferably removed from the printed circuit board 20 transversely to the first axis Z. After removal of the clamping unit 200, the printed circuit board 20 and / or preferably the first and second half shells H 1 and H 2 are exposed at the clamping point.The housing 60 is then closed at the clamping point. This means that the region which could not be injection molded in order to hold the printed circuit board 20 is also now closed. The clamping point is preferably closed by means of a welding mandrel 61 and a welding cover 62 (see FIG. 4 ). When closing the housing 60 with the aid of the welding mandrel 61 and the welding cap 62, an ultrasonic welding method is preferably used. Of course, other joining methods known to the skilled person can also be used, such as, for example, adhesive bonding, provided these are compatible with applicable hygiene regulations.List of reference characters10 Electronics unit 20 Printed circuit board 21 First axial end 22 Second axial end 23 First plate side 24 Second plate side 25 First through-opening 26 Second through-opening 27 Bracket 30 Transmitting coil 40 Receiving coil 50 Temperature sensor 60 Housing 61 Welding mandrel 62 Welding cover 100 Inductive conductivity sensor 200 Clamping unit 201 First tool core 202 Second tool core DI 1 First through-opening inner diameter DI 2 Second through-opening inner diameter EI Receiving coil inner diameter GD Housing thickness RF 1 First annular surface RF 2 Second annular surface SI Transmitting coil inner diameter Z First axis H 1 First half shell H 2 Second half shell

Claims

Inductive conductivity sensor (100) comprising: - an electronics unit (10) comprising a printed circuit board (20), a transmitting coil (30), a receiving coil (40) and a temperature sensor (50), wherein the printed circuit board (20) extends along a first axis (Z) and has a first axial end (21) and a second axial end (22), wherein the printed circuit board (20) has a first board side (23) and a second board side (24), a first through-opening (25) and a second through-opening (26), wherein the first through-opening (25) is arranged between the first axial end (21) and the second axial end (22) of the printed circuit board (20) and the second through-opening (26) is arranged between the first axial end (21) and the first through-opening (25), such that a bracket (27) is formed between the first axial end (21) and the second through-opening (26), wherein the temperature sensor (50) is arranged on the bracket (27), wherein the transmitting coil (30) is arranged on the first plate side (23) around the first through-opening (25) and the receiving coil (40) is arranged on the second plate side (24) around the first through-opening (25), - a housing (60) which encloses the electronics unit (10) in a fluid-tight manner, such that a fluid can flow through the first through-opening (25) and the second through-opening (26) in each case at least partially.Inductive conductivity sensor (100) according to claim 1, wherein the housing (60) is integrally connected to the electronics unit (10) by an injection molding process.Inductive conductivity sensor (100) according to claim 1 or 2, wherein the housing (60) has a housing thickness (GD) and the housing thickness (GD) is less than 2 mm, preferably less than 1 mm, at least above the temperature sensor (50).Inductive conductivity sensor (100) according to one of the preceding claims, wherein the transmitting coil (30) has a transmitting coil inner diameter (SI), the receiving coil (40) has a receiving coil inner diameter (EI) and the first through-opening (25) has a first through-opening inner diameter (DI1), wherein the transmitting coil inner diameter (SI) and the receiving coil inner diameter (EI) are larger than the first through-opening inner diameter (DI1).Inductive conductivity sensor (100) according to one of the preceding claims, wherein the first through opening (25) has a first through opening inner diameter (DI1) and the second through opening (26) has a second through opening inner diameter (DI2), wherein the second through opening inner diameter (DI2) is equal to the first through opening inner diameter (DI1) or greater than the first through opening inner diameter (DI1).Method for producing an inductive conductivity sensor (100), comprising: - providing an electronics unit (10) and an injection mould, wherein the electronics unit (10) has a printed circuit board (20), a transmitting coil (30), a receiving coil (40) and a temperature sensor (50), wherein the printed circuit board (20) extends along a first axis (Z) and has a first axial end (21) and a second axial end (22), wherein the printed circuit board (20) has a first board side (23) and a second board side (24), a first through-opening (25) and a second through-opening (26), wherein the first through-opening (25) is arranged between the first axial end (21) and the second axial end (22) of the printed circuit board and the second through-opening (26) is arranged between the first axial end (21) and the first through-opening (25), such that a bracket (27) is formed between the first axial end (21) and the second through-opening (26), wherein the temperature sensor (50) is arranged on the bracket (27), wherein the transmitting coil (30) is arranged on the first plate side (23) and the receiving coil (40) is arranged on the second plate side (24) in each case around the first through-opening (25), - fixing the electronics unit (10) relative to the injection mold with the aid of a clamping unit (200), wherein the clamping unit (200) clamps the printed circuit board (20) at a clamping point, - injecting a plastic material for forming a housing (60) of the inductive conductivity sensor (), - removing the clamping unit (200), - closing the housing (60) at the clamping point.The method for manufacturing an inductive conductivity sensor (100) according to claim 6, wherein the clamping unit (200) clamps the circuit board (20) to the first through hole (25).Method for producing an inductive conductivity sensor (100) according to Claim 6 or 7, wherein the transmitting coil (30) has a transmitting coil inner diameter (SI), the receiving coil (40) has a receiving coil inner diameter (EI) and the first through-opening (25) has a first through-opening inner diameter (DI1), wherein the transmitting coil inner diameter (SI) and the receiving coil inner diameter (EI) are greater than the first through-opening inner diameter (DI1) such that a first annular surface (RF1) is formed on the first plate side (23) and a second annular surface (RF2) is formed on the second plate side (24), wherein the clamping unit (200) clamps the printed circuit board (20) to the first annular surface (RF1) and the second annular surface (RF2).Method for producing an inductive conductivity sensor (100) according to one of Claims 6 to 8, wherein the electronics unit (10) has a first half shell (H1) and a second half shell (H2), which are arranged in such a way that the transmitting coil (30) and the receiving coil (40) are protected, and the clamping unit (200) clamps the printed circuit board (20) to the first half shell (H1) and to the second half shell (H2) when fixing the electronics unit (10).Method for producing an inductive conductivity sensor (100) according to Claim 9, wherein a welding mandrel (61) and a welding cap (62) are used when closing the housing (60) at the clamping point, wherein the welding mandrel (61) and the welding cap (62) are welded to the housing (60) by means of an ultrasonic method.

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