Water tank with liquid level sensor, combination of tank and base, and method for detecting level of water in a tank

Abstract

The present application concerns a tank for water, preferably purified water of at least ASTM type III grade, and a combination of a tank with a base as well as a method for detecting a level of water, preferably purified water of at least ASTM type III grade, in a tank, the tank intended to be used in a laboratory environment and / or in conjunction with a water purification system.

Description

[0001] WATER TANK WITH LIQUID LEVEL SENSOR, COMBINATION OF TANK AND BASE, AND METHOD FOR DETECTING LEVEL OF WATER IN A TANK

[0002] Technical Field

[0003] The present application concerns a tank for water, preferably purified water of at least ASTM type III grade, and a combination of a tank with a base as well as a method for detecting a level of water, preferably purified water of at least ASTM type III grade, in a tank, the tank intended to be used in a laboratory environment and / or in conjunction with a water purification system.

[0004] Background

[0005] There are several types of water purity available depending on the intended use in a laboratory environment. For example, the American Society for Testing and Materials (ASTM) uses D1193-06 and has four grades of water. This includes a range from Type III for general use up to Type 1+ for sensitive applications. The highest purity water, often denoted as "ultrapure" or in accordance with ASTM D 1193-06 as "Type I" water, is, for example, characterized by a resistivity of at least 18.0 MQ • cm and at most 5 ppb of total organic carbon (TOC). "Type II" water is typically characterized by a resistivity of at least 1.0 MQ • cm and at most 50 ppb of total organic carbon. "Type III" water is the lowest quality water grade for laboratory use, having a resistivity of at least 0.05 MQ • cm and at most 200 ppb of total organic carbon, and is recommended for standard laboratory use, such as for glassware rinsing or heating baths, as well as a feed to water purification systems producing Type I water.

[0006] An alternative specification of water purity levels provided by the International Organization for Standardization (ISO) is based on ISO 3696:1987 and specifies three grades of water: Grade 1, Grade 2 and Grade 3, where Grade 1 is the purest.

[0007] In more detail, ASTM Type I grade water, also known as "ultrapure water", is the purest form of water to be produced. It is used for the most critical applications and advanced analytical procedures including cell culture or tissue culture, liquid chromatography, gas chromatography, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Graphite Furnace Atomic Absorption Spectrometry (GF-AAS), molecular biology. Type I grade water can also be used in applications that require Type II grade water. ASTM Type II grade water, often referred to as "purified water", has a lower pureness than Type I grade water, but still maintains high levels of purity. It is a suitable feed water for clinical analyzers as the calcium build-up is reduced with this water type. It can also be used in applications such as general lab practices (media preparation or buffer creation), microbiological analysis and preparation, electrochemistry, general spectrophotometry or can also be used as feed water for Type I grade water production.

[0008] ASTM Type III grade water, also known as "primary grade water" or "RO water" (as frequently produced by reverse osmosis), is water produced through the reverse osmosis purification technology. Of all the pure water types it has the lowest level of purity, but is typically the starting point for basic lab applications, such as cleaning glassware, filling water baths or media preparation or feeding autoclaves. It can also be used as a feed water for Type I grade water production.

[0009] The purified water is commonly produced in a water purification system and stored in a tank for use in the laboratory environment. In this context the system is commonly implemented with an automatic detection of the liquid (water) level in the tank to control the purification process, at least in order to detect an upper liquid (water) level in the tank that triggers a stop of production of purified water.

[0010] A liquid level sensor is often built into a system and relies on sensor technology that evaluates pressure or weight of the water in the tank, or uses ultrasonic or laser radiation to detect the presence / absence of liquid at a certain position. Capacitive sensor technology for liquid detection is also known as such.

[0011] In ultrapure water applications, however, the level sensor must not come in direct contact with the purified water in order to avoid contamination. This criterion renders the use of a pressure sensor less desirable as it requires direct contact with the purified water. While the capacitive sensor in principle could be implemented without direct contact with water in that the sensor is arranged outside the tank in a frame of a base, which is in particular advantageous if the tank is to be mobile and transportable, experiments demonstrated that the capacitive sensor in such an arrangement is not accurate enough to measure the water level inside the tank.

[0012] EP 2 489 996 Al discloses a household appliance with a capacitive level sensor and with a removable tank for holding water. The level sensor comprises an electrode arrangement which, when the tank is inserted into a base, rests against an outside wall of the tank. Measuring electrodes are provided on the electrode arrangement in order to measure the fill level of the tank using capacitive technology.

[0013] EP 3 405 756 Bl discloses a household appliance, which comprises a housing and a container which can be uncoupled from the housing. A capacitive fill level sensor is arranged on the housing and is configured to determine a capacity value which depends upon a fill level of matter in the container. A distance sensor which comprises an inductive distance sensor is provided to determine a distance value which depends upon a distance between the fill level sensor and the container. A processing unit is provided which is configured to determine a value for the fill level on the basis of the capacity value and on the basis of the distance value. The distance sensor comprises a sensor unit, which is arranged on the housing and is configured to generate an electromagnetic field; and an influencing unit, which is arranged on the container and is configured to influence the electromagnetic field, in particular to attenuate it.

[0014] US 2017 / 119970 Al discloses a medication injector for dispensing liquid medications to people that includes a container which is filled with the liquid and which has an opening at one end for dispensing the liquid and at least one pair of capacitive measuring electrodes disposed opposite each other in the outer region of the container, in particular on the wall, for determining the permittivity of the respective medium in the intermediate region between the measuring electrodes. The measuring electrodes are used by the injector to determine the fill level of the container. A shielding surrounds the measuring electrodes in the manner of a sheath, is disposed around the container, and reduces possible external interfering influences on the capacitive measurement, such as those resulting from contact, for example.

[0015] DE 10 2015 203 744 Al discloses a tank comprising walls, which in turn comprise electrically conductive plates with electrical connectors and means for capturing a signal, particularly for determining the filling level, wherein the walls comprise electrically conductive plastic as plates. Due to the tank comprising both, conductive and non-conductive plastic, its production is rather complicated.

[0016] US 2022 / 0170775 Al discloses a device for taking capacitive measurements of a height of a fluid in a tank, the device comprising at least one pair of capacitors extending in a longitudinal direction intended to be parallel to the normal to the free surface of the fluid. US 2020 / 0189383 Al discloses a liquid fuel tank comprising a plurality of liquid level detection capacitive sensors, wherein the fuel tank is electrically conductive and each liquid level detection capacitive sensor comprises an electrically insulating plate each arranged thickness-wise between each capacitive sensor and the fuel tank.

[0017] US 2023 / 0110343 Al relates to a liquid level sensor for detecting a level of milk in a milk bottle, wherein the liquid level sensor may be a capacitive sensor.

[0018] JP 4967673 B2 discloses a liquid container for an electric device detecting the presence of absence and liquid level of a liquid stored in the liquid container by measuring a change in capacitance with a capacitance detection circuit.

[0019] However, neither of these documents discloses liquid level sensing for highly purified water, such as of ASTM type III grade water or of even higher purify, such as ASTM type II or I grade water. Furthermore, all of these require wired connections, thus rendering these liquid tanks unsuitable for being easily moved from one place to another, for example, from one laboratory to another.

[0020] The present application aims at providing a tank for water, a combination of a tank with a base, as well as a method for detecting a level of water in a tank, wherein the level detection is particularly suitable for purified water of at least ASTM type III grade, preferably for purified water of at least ASTM type II grade or ASTM type I grade, and, preferably, for a mobile tank.

[0021] Summary

[0022] To solve the problem the present application provides a tank with the features of claim 1, a combination of a tank with a base with the features of claim 14, and a method for detecting a level of water in a tank with the features of claim 15. Preferred embodiments or variants are defined in the respective dependent claims.

[0023] The present application in particular provides a tank for water, preferably purified water of at least ASTM type III grade, preferably for purified water of at least ASTM type II grade, the tank comprising a wall surrounding a volume for receiving the water, and a liquid (water) level sensor device for detecting at least one level of the water in the volume. The liquid (water) level sensor device comprises, for each level of the water to be detected, at least one pair of electrodes forming a capacitor arranged to undergo a change of capacitance on proximity of the water, the electrodes embedded in the wall material so as to be shielded from contact with the water in the volume.

[0024] The level detection in the water tank as described herein is based on the capacitive technology or principle. The capacitive principle is based on change of capacitor link to the water. The dielectrics of air and water are different, i.e. the dielectric of air is around 1 and that of the water is around 80. The electrical field between the electrodes creates a capacitor.

[0025] The standard for a capacitive sensor is a RLC resonant circuit. When the capacitive sensor changes, the resonant frequency changes. The capacitive sensor has a high sensibility when the electrodes are close to the water. For the water tank as defined herein a very thin plastic material layer film of the wall material is used in an aim to reduce the distance between electrodes and the water. The RLC resonant circuit is thus used like in a traditional approach of a capacitive sensor. It is noted that the term "RLC circuit" denotes an electric circuit consisting of a resistor R, an inductor L, and a capacitor C, connected in series or in parallel.

[0026] Preferably, a smallest thickness of the wall material between the electrodes and an inner surface of the wall in contact with the water in the volume is at most 500 pm, preferably at most 175 pm, more preferably at most 150 pm, even more preferably at most 120 pm, and most preferably at most 100 pm.

[0027] Preferably, the smallest thickness of the wall material is at least 50 pm, more preferably at least 70 pm, and most preferably at least 90 pm.

[0028] By reducing the thickness of the wall material between the electrodes and the water, the accuracy of the detection is increased while maintaining the complete separation of the water and the sensor device. Independent from the shape of the electrodes there is a tendency that, when the thickness of the plastics material between the electrodes and the water increases, the capacitor change between air and water decreases exponentially.

[0029] Preferably, the electrodes of each pair form a coplanar capacitor. For the coplanar capacitor; the dielectric is the liquid (water) inside the tank. When the electrodes of the sensor device are above the water level, for example, when the tank is empty, the dielectric is that of air (around 1). On the other hand, when the electrodes of the sensor device are below the water level, for example, when the tank is full of water, the dielectric is around 80. When the dielectric changes, the capacitor value changes.

[0030] Preferably, the electrodes of each pair are formed by rectangular, spiral, interdigital, or meandered conductive layers. While the design shapes of the electrodes provide a different sensibility with more complex shapes generally providing better sensitivity, rectangular and interdigital shapes are preferred for reason of simpler implementation, whereas the interdigital shape is often used to detect humidity and gives better detection results than the rectangular shape.

[0031] In particular, the shape shall enable to detect few millimeters of water inside the tank and shall avoid detecting condensed water (i.e. shall be robust to condensation).

[0032] Preferably, the sensor device of the tank comprises an inductor, preferably a coil or an antenna, connected to the at least one pair of electrodes, for transmission of signals to a complementary inductor of a circuitry for signal evaluation outside the tank using a wireless transmission protocol. One (first) inductor is inside the tank close to the capacitive sensor and the other (second) inductor is outside the tank. This second inductor is preferably placed as close as possible to the first inductor. For example, the second inductor may be placed at a distance of around 6 mm from the first inductor inside the tank wall.

[0033] An advantage of the embedding of the sensor, for example by an in-mold-labelling process into the thickness of the tank wall, and the use of a wireless technology for the communication between the tank and an external circuitry constituting a semiconductor signal conditionerthrough mutual inductors, is that no active electronic component is used inside the tank which avoids any contamination of the water in the tank. Additionally, the absence of active electronic components in the tank reduces the need for maintenance as well as the complexity of manufacturing.

[0034] Preferably, a shielding for an electromagnetic field is arranged in the wall material on a side of the electrodes located away from an / the inner surface of the wall in contact with the water in the volume. The presence of the shielding provides the effect that the electrical field between the electrodes is focused inside the tank. Such shielding can either be arranged inside or outside the tank wall. However, as the distance between the electrodes and the shielding is only the thickness of one or two insulating ink layers, i.e. is typically from about 10 pm to about 20 pm, the addition of such shielding renders the sensor less sensitive. Therefore, it is preferred to arrange the shielding outside the tank, and preferably on the frame (base of the tank).

[0035] Preferably, the components of the sensor device on the side of the tank including the electrodes and preferably a / the shielding and / or a coil and / or an antenna of the sensor device are formed by conductive ink printed on a flexible substrate, preferably a film with a thickness of 120 pm or less, preferably 70 pm or less, preferably a film made of plastic or paper or a combination of the two. The conductive ink can be silver ink or copper ink printed with a thickness of at least 10 pm onto the substrate.

[0036] By implementing the components of the sensor device on the side of the tank as printed components on a thin substrate / film, the distance between water and electrode is further reduced.

[0037] Preferably, the tank further comprises a protective layer or film formed on the printed conductive ink to avoid abrasion of the ink deposit during embedding, preferably molding, into the wall material. This measure compensates a potential downturn of using the very thin printed components integrated into the tank wall material caused by a relative movement of the liquid (molten) plastics material and the sensor device during the typical manufacturing process in a mold, e.g. an injection mold, because the substrate / film is typically placed inside the mold before the plastics material is injected.

[0038] The tank may be at least partly made from a molded plastics material, preferably a non- conductive plastics material, especially polypropylene or polyethylene or polyamide or PET, at least in a region where the sensor device is embedded, and / or is at least partly made from a transparent or translucent material.

[0039] The use of a plastics material allows a production of the tank at low cost and with the required thin wall thicknesses. Using transparent or translucent plastics material at least in certain parts of the tank provides the possibility of a visual detection, for example by the naked eye of a user, of the content or filling level inside the tank from outside. This aspect can be used for a very basic embodiment that uses the sensor device for the automatic detection of a single filling level in the tank which can be either a rated maximum filling level or a rated minimum filling level whereas the respective other filling level is monitored by the user. In order to automate the detection of the maximum and minimum filling levels in the tank, the sensor device may comprise two pairs of electrodes forming two capacitors spaced apart from each other in a height direction of the volume of the tank. Further pairs of electrodes may be used if additional filling levels are to be monitored and detected.

[0040] The electrodes of the two or more capacitors are preferably connected with each other in a parallel arrangement. In this case the overall capacitor value is the sum of each sensor, and only one detection channel is needed to detect two or more filling levels.

[0041] The electrodes of the two (or more) capacitors can be connected with each other through conductive tracks formed by conductive ink printed onto a / the flexible substrate. The conductive tracks are preferably twisted with each other along their axial extension.

[0042] Preferably, the herein described tank is configured to be mobile to be handled and transported by a user. This embodiment, in particular in conjunction with the wireless transmission of the sensor signals to an external detection or evaluation circuitry provides for a very simple and intuitive handling of the tank in the context of laboratory processes.

[0043] The present application also provides a combination of a tank and a base, wherein the tank is the tank as described herein and the base is configured to support the tank in a defined position. The base comprises a circuitry for signal evaluation for detecting the proximity of the water at the at least one level of the water in the volume based on the change of capacitance of the sensor device of the tank, and the circuitry is arranged outside the tank, for example in the base, and is configured to be coupled with the sensor device of the tank through wires or, more preferably, through complementary inductors using wireless transmission (which may be implemented using coils or antennas; RFID or NFC).

[0044] Finally, the present application also provides a method for detecting a level of water, preferably purified water of at least ASTM type III grade, in a tank in a laboratory environment, the method comprising the steps of

[0045] (a) providing a tank as defined herein;

[0046] (b) introducing the water into the tank until reaching the at least one pair of electrodes defining a first level of water in the tank;

[0047] (c) optionally, if mobile, moving the tank to a desired location; and

[0048] (d) withdrawing liquid (water) from the tank until reaching a second level of water in the tank that is lower than the first level, the second level preferably defined by a second pair of electrodes to be automatically detected or through a visual manual inspection in a very basic implementation.

[0049] Additionally, the present application provides for a method for producing such tank, the method comprising the steps of

[0050] (a') providing an injection mold for molding the tank of claim 1;

[0051] (b') inserting one or more liquid (water) level sensor device (2) into the injection mold, the one or more liquid (water) level sensor device (2) comprising, for each level of the water to be detected, at least one pair of electrodes (3;4) forming a capacitor arranged to undergo a change of capacitance on proximity of the water, the electrodes (3;4) embedded in the wall (la) material so as to be shielded from contact with the water in the volume.

[0052] Brief description of the drawings

[0053] Preferred embodiments of the present device and system will now be described with respect to the following attached exemplary, schematic, and non-limiting drawings:

[0054] Figure la is a schematic perspective view of a tank according to an embodiment.

[0055] Figure lb is a schematic perspective view of a tank according to another embodiment.

[0056] Figure 2 is a schematic cross-sectional view of a tank and a base according to an embodiment in a zone containing the sensor device.

[0057] Figure 3 is a view of two pairs of electrodes connected in series.

[0058] Figure 4 is an equivalent schematic diagram of the components of the sensor device and the detection circuit according to an embodiment.

[0059] Figure 5 is a schematic view of two variants of wireless sensor devices with pairs of electrodes connected in series.

[0060] Figure 6 is a schematic cross-sectional view of a tank and a base according to a variant of Figure 2 in a zone containing the sensor device. Detailed description

[0061] The tank 1 for water, preferably purified water of at least ASTM type III grade, more preferably of at least ASTM type II grade, and most preferably of ASTM type I grade, as defined herein in the most general setup is shown in Figures la and lb in a schematic perspective view. The tank 1 has a wall la surrounding a volume for receiving the water W and air A, and one or more liquid (water) level sensor device 2 for detecting one or more level / levels of the water W in the volume. To give an example, in case of a mobile tank, the volume of such tank may be between 2 I and 10 I, preferably around 5 I. The tank 1 is preferably configured to be mobile to be handled and transported by a user between a water purifier station or water purifier device and a workbench where the water is dispensed and used, although the principles implemented may also be realized in a stationary tank or large tank. The tank 1 has no electric power supply and is thus a "passive" component in the combination of the tank 1 with a base 12 described later. The tank being "passive" greatly facilitates use and also renders the tank essentially maintenance-free.

[0062] The liquid (water) level sensor device 2 comprises, for each level of the water to be detected, at least one pair of electrodes 3,4 forming a capacitor arranged to undergo a change of capacitance on proximity of the water. The electrodes 3,4 are embedded or integrated, preferably by being insert molded (for example, by in-mold labelling), into the material of the wall la so as to be shielded from contact with the water in the volume. If plural capacitors are provided they are spaced apart from each other in a height direction of the volume of the tank.

[0063] In the examples of Figures la and lb two pairs of electrodes for detecting two different filling levels of the water in the tank's volume (i.e. a high and a low level) are shown. However, variants with only a single pair of electrodes forming a single capacitor or with more than two pairs of electrodes forming more than two capacitors are to be comprised within the present disclosure.

[0064] The electrodes 3,4 of each pair of electrodes form a coplanar capacitor and are in this example formed by rectangular conductive layers 3a, 3b, 4a, 4b. The electrodes of the respective pair of electrodes extend parallel to each other (with a width of about 25 mm as an example of a tank for a mobile application) and over or at the typical filling height of the water in the tank volume (with a height of about 300 mm for a high-level detection or only several mm from the bottom of the tank as an example for a low-level detection). The electrodes in the variant of Figure la extend vertically over a desired detection height whereas the electrodes in the variant of Figure lb extend horizontally at the desired detection levels. Other shapes of electrodes with spiral, interdigital, or meandered conductive layers are to be comprised within the present disclosure to form the respective capacitors.

[0065] Experiments have shown that the temperature and the gap width between the electrodes of each capacitor can be neglected as influence on the capacitor change from air to water. However, the width of the electrodes and the electrode area may have a significant influence with larger widths and increased areas creating larger capacitor changes.

[0066] As shown in Figure 2 the entire liquid (water) level sensor device 2 is integrated and embedded in the material of the wall la of the tank at an appropriate location for the level detection such that a smallest thickness e5 of the material between the electrodes 3,4 and an inner surface of the wall la (i.e. measured perpendicular between the surface of the outer surface of the electrodes and the inner surface of the tank wall) that is, in use, in contact with the water in the volume is at most 500 pm, preferably at most 175 pm, more preferably at most 150 pm, even more preferably at most 120 pm, and most preferably at most 100 pm. Preferably, the smallest thickness of the wall material is at least 50 pm, more preferably at least 70 pm, and most preferably at least 90 pm.

[0067] Although not shown in Figure 2, the liquid (water) level sensor device 2 may comprise a shielding for an electromagnetic field that is also arranged in the material of the wall la on a side of the electrodes 3,4 located away from the inner surface of the wall that is in contact with the water in the volume. The shielding may be a separate element, for example in the form of a layer, grid or net or may be a component that is integrated with the sensor device 2.

[0068] As shown in Figures 2 and 4 the sensor device 2 of the tank 1 embedded into the wall material comprises an inductor 6a, preferably in the form of a coil or an antenna, that is connected to the pairs of electrodes 3,4, for transmission of signals to a complementary inductor 6b, preferably in the form of a coil or an antenna, of a circuitry 20 for signal evaluation outside the tank 1 using a wireless transmission.

[0069] In order to secure the embedding of the entire liquid (water) level sensor device 2 into the wall material while achieving the reduced distance between the electrodes and the water and without unduly thickening the wall, the components of the level sensor device 2 including the electrodes 3,4 and preferably, if provided, the shielding and the inductor 6a in the form of the coil or the antenna are preferably formed by conductive ink printed on a thin flexible substrate 11. The flexible substrate 11 preferably is a film with a thickness of 120 pm or less, preferably 70 pm or less, and preferably is a film made of plastic or paper or a combination of the two (Figure 6 shows a variant wherein the thin flexible substrate 11 includes a plastic / paper printing support sheet 14.). This substrate / film is placed inside a mold before injecting the plastics material that is to form the side walls of the tank (insert molding or in-mold-labelling process).

[0070] The tank 1 may be completely or partly made from a plastics material, preferably from a non-conductive plastics material, for example polypropylene or polyethylene or polyamide or PET, at least in a region where the sensor device (2) is embedded. If visibility of the content and filling level from the outside is desired (for example in the most basic implementation with only a single level detection), the tank may be completely or at least partly (for example in the form of a window) made from a transparent or translucent material.

[0071] The conductive ink, as is known as such, may be a silver-comprising ink or a copper- comprising ink (generally simply referred to as "silver ink" and "copper ink") printed with a thickness of at least 10 pm onto the substrate 11. The lower conductivity of silver versus copper shall be taken into account when determining the coil geometry and coil dimensions as well as the number of printing passes defining the ink thickness. Each printed layer of ink may be around 10 pm thick, so that, with two layers of ink printed above each other, the thickness is about 20 pm and the electronic track resistivity is lower so that the coil will have a better Q coefficient.

[0072] As shown in the variant of Figure 6, the sensor device 2 or the circuitry 20 may further comprise an optional isolating protective layer or film 13 formed on the printed conductive ink to avoid mechanical abrasion of the ink deposit during embedding, preferably molding, into the wall material during the plastic injection phase. Such protective layer 13 may be added to the sensor device 2 after printing of the functional components. It will follow the contour thereof and will increase the robustness during handling. The protective layer or film 13 may be formed by printing a further layer of ink with insulating properties.

[0073] Depending on the embedding depth of the sensor device 2 in the wall of the tank and that of the circuitry 20 for signal evaluation for detecting the proximity of the water in the base 12 for receiving the tank 1 in the mounted position, the inductor-to-inductor (coil-to-coil) spacing e6 is slightly larger than the air gap e2 between the tank's outer wall la in the zone of the sensor device 2 and the base 12.

[0074] As shown in Figure 2 a shield 10 may be provided inside the wall la of the tank, but may also be provided inside a wall 12a of the base 12 and may be formed on a substrate 9 of the circuitry 20. Since the space constraints on the side of the base are not as strict as on the side of the tank, the circuitry 20 may be formed on a common PCB (Printed Circuit Board) but may also be implemented in the form of a thin flexible substrate onto which the components are printed by conductive ink as described above in connection with the sensor device 2. This helps to reduce the overall thickness el of the base wall and protects the circuitry 20 from the environment while maintaining the function of wireless communication of the signals between the mating inductors 6a, 6b.

[0075] If two pairs of electrodes 3,4 forming two capacitors spaced apart from each other in the height direction of the volume of the tank 1 are provided in order to detect a high-level and a low level of the water in the volume, the level detection may be done with two separate acquisition channels (meaning that the sensor device 2 and the circuitry 20 for signal evaluation are provided with two separate sensor-evaluation channels). For the purposes of simplification and cost reduction, the high and low level channels may be integrated in a single channel, where each sensor works as a capacitor and the electrodes 3,4 of two sensors are connected in parallel (see Figures 3 to 5). The overall capacitor value is then the sum of each sensor. Figure 5 shows an example where the two parallel capacitors 3,4 (sensors) and the single coil of the inductor 6a are printed on a common substrate 11.

[0076] Figure 4 shows an equivalent schematic diagram of the components of the sensor device 2 and the detection circuit 20 arranged in a working posture (i.e. when the tank 1 is received in the base 12) according to an embodiment with two capacitors 3,4 connected in parallel. The sensor device 2 and the detection circuit 20 are respectively provided with an inductor 6a, 6b (in the form of a coil) for the wireless signal transmission and both circuits shall have the same resonant frequency for improved communication. In this diagram, reference numeral 5 represents a parallel parasitic resistor of the ink of the sensor device 2, 8 is a common coil filter or common mode choke for EMC purpose, capacitor 7a is used for the main resonant frequency selection, and capacitor 7b is used for EMC purposes. On the side of the detection circuit 20 a capacitance-to-digital converter of the Texas Instruments FDC2xlx family may be used to implement the capacitive sensing application and signal evaluation of the present application. Where the two parallel capacitors of the sensor device 2 are connected by a straight wire or a simple straight printed conductive track 21a, 21b on the flexible plastic substrate to provide for a low-level and high-level detection inside the tank's volume (see the example on the left side of Figure 5), the connecting tracks or wires 21a, 21b beyond a certain length could form an antenna that creates an EMC issue. As a counter-measure, the straight printed track may be replaced by a twisted track in which the conductive tracks 21a, 21b are twisted with each other along their axial extension as shown in the example on the right side of Figure 5. To avoid a short-circuit, a non-conductive dielectric intermediate material / layer 21c must be provided between the conductive layer and conductive tracks at the positions of overlap. Such non-conductive dielectric material / layer may be applied, for example, by using dielectric ink in a separate printing pass.

[0077] The tank (1) as defined herein may be produced by a method comprising the steps of (a') providing an injection mold for molding the tank (1) as defined herein;

[0078] (b') inserting one or more liquid (water) level sensor device (2) into the injection mold, the one or more liquid (water) level sensor device (2) comprising, for each level of the water to be detected, at least one pair of electrodes (3;4) forming a capacitor arranged to undergo a change of capacitance on proximity of the water, the electrodes (3;4) embedded in the wall (la) material so as to be shielded from contact with the water in the volume.

[0079] By using "passive" components, i.e. not requiring an electric power supply the tank comprising the liquid level sensor as defined herein offers a number of advantages over the conventionally known technology, notably that it greatly facilitates use, for example, by rendering it easily removable and transportable (without having to detach and attach wire connections and / or electrical supply) and also renders the tank essentially maintenance- free. It furthermore renders the manufacturing of such tanks comprising the liquid level sensor as described herein more simple in terms of manufacturing.

Claims

Claims1. A tank (1) for water, preferably purified water of at least ASTM type III grade, the tank (1) comprising(i) a wall (la) surrounding a volume for receiving the water (W); and(ii) a liquid level sensor device (2) for detecting at least one level of the water (W) in the volume, wherein the liquid level sensor device (2) comprises, for each level of the water to be detected, at least one pair of electrodes (3;4) forming a capacitor arranged to undergo a change of capacitance on proximity of the water, the electrodes (3;4) embedded in the wall (la) material so as to be shielded from contact with the water in the volume.

2. The tank (1) according to claim 1, wherein a smallest thickness (e5) of the wall (la) material between the electrodes (3;4) and an inner surface of the wall (la) in contact with the water in the volume at most 500 pm, preferably at most 175 pm, more preferably at most 150 pm, even more preferably at most 120 pm, most preferably at most 100 pm, and preferably at least 50 pm.

3. The tank (1) according to claim 1 or 2, wherein the electrodes (3;4) of each pair form a coplanar capacitor.

4. The tank (1) according to any one of claims 1 to 3, wherein the electrodes (3;4) of each pair are formed by rectangular, spiral, interdigital, or meandered conductive layers (3a,3b;4a,4b).

5. The tank (1) according to any one of claims 1 to 4, wherein a shielding for an electromagnetic field is arranged in the wall (la) material on a side of the electrodes (3;4) located away from an / the inner surface of the wall (la) in contact with the water in the volume.

6. The tank (1) according to any one of claims 1 to 5, wherein the tank (1) is at least partly made from a plastics material, preferably polypropylene or polyethylene or polyamide or PET, at least in a region where the sensor device (2) is embedded, and / or is at least partly made from a transparent or translucent material.

7. The tank (1) according to any one of claims 1 to 6, wherein the sensor device (2) of the tank (1) comprises an inductor (6a), preferably a coil or an antenna, connected to the at least one pair of electrodes (3;4), for transmission of signals to a complementary inductor (6b) of a circuitry (20) for signal evaluation outside the tank (1) using a wireless transmission protocol.

8. The tank (1) according to any one of claims 1 to 7, wherein the sensor device (2) comprises two pairs of electrodes (3;4) forming two capacitors spaced apart from each other in a height direction of the volume of the tank (1), the electrodes (3;4) of the capacitors preferably connected with each other in a parallel arrangement.

9. The tank (1) according to claim 8, wherein the electrodes (3;4) of the two capacitors are connected with each other through conductive tracks formed by conductive ink printed onto a / the flexible substrate (11), the conductive tracks being preferably twisted with each other along their axial extension.

10. The tank (1) according to any one of claims 1 to 9, wherein the electrodes (3;4) and preferably a / the shielding and / or a / the inductor (6a) in the form of a coil or an antenna of the sensor device (2) are formed by conductive ink printed on a flexible substrate (11), preferably a film with a thickness of 120 pm or less, preferably 70 pm or less, preferably a film made of plastic or paper or a combination of the two.

11. The tank (1) according to claim 10, further comprising a protective layer or film formed on the printed conductive ink to avoid abrasion of the ink deposit during embedding, preferably molding into the wall (la) material, preferably wherein the conductive ink is silver ink or copper ink printed with a thickness of at least 10 pm onto the substrate (11).

12. The tank (1) according to any one of claims 1 to 11, wherein the tank (1) is configured to be mobile to be handled and transported by a user.

13. A combination of a tank (1) and a base (12), wherein the tank (1) is the tank according to any one of claims 1 to 12, the base (12) is configured to support the tank (1) in a defined position, and the base (12) comprises a circuitry (20) for signal evaluation for detecting the proximity of water at the at least one level of the water in the volume based on the change of capacitance of the sensor device (2) of the tank (1), the circuitry (20)arranged outside the tank (1) and configured to be coupled with the sensor device (2) of the tank (1) through wires or through complementary inductors (6a, 6b) using a wireless transmission protocol.

14. A method for detecting a level of water, preferably purified water of at least ASTM type III grade, in a tank (1), the method comprising the steps of(a) providing a tank (1) according to any one of claims 1 to 12;(b) introducing water into the tank (1) until reaching the at least one pair of electrodes (3;4) defining a first level of water in the tank (1);(c) optionally, if mobile, moving the tank (1) to a desired location; and(d) withdrawing liquid from the tank (1) until reaching a second level of water in the tank (1) that is lowerthan the first level, the second level preferably defined by a second pair of electrodes (4).

15. A method for producing the tank (1) of claim 1, the method comprising the steps of (a') providing an injection mold for molding the tank (1) of claim 1;(b') inserting one or more liquid level sensor device (2) into the injection mold, the one or more liquid level sensordevice (2) comprising, foreach level of the water to be detected, at least one pair of electrodes (3;4) forming a capacitor arranged to undergo a change of capacitance on proximity of the water, the electrodes (3;4) embedded in the wall (la) material so as to be shielded from contact with the water in the volume.

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