Conductivity / Resistivity Cell, Water Purification System, and Method for Determining the Conductivity and / or Resistivity of a Sample Liquid

Abstract

The present invention relates to a conductivity / resistivity cell, preferably for use in a water purification system, a water purification system comprising a conductivity / resistivity cell, and a method for determining the conductivity and / or resistivity of a sample liquid.

Description

[Technical Field]

[0001] The present invention relates to a conductivity / resistivity cell, preferably for use in a water purification system, a water purification system comprising a conductivity / resistivity cell, and a method for determining the conductivity and / or resistivity of a sample liquid. [Background technology]

[0002] Conductivity / resistivity is an analytical parameter widely used in water purity analysis, reverse osmosis monitoring, cleaning procedures, chemical process control, industrial wastewater treatment, etc.

[0003] A conductivity sensor, also known as a conductivity probe or conductivity electrode, is an analytical instrument that measures a solution's ability to conduct electrical current. The presence of ions in a solution gives the solution conductivity. The higher the concentration of ions, the higher the conductivity. In some applications, purity is measured as resistivity (the reciprocal of conductivity). The terms "conductivity sensor," "conductivity probe," and "conductivity cell" are considered synonymous in the context of this disclosure, and for simplicity, the term "cell" is used consistently.

[0004] A conductivity / resistivity cell in the context of this disclosure is a flow-through device for use in a water purification system. A conductivity / resistivity cell typically contains one or two pairs of "conductivity electrodes" arranged in a flow path through which the liquid under test flows, where the liquid under test contacts the electrodes and the signal is evaluated by an electronic device (controller or meter) to determine or measure the conductivity / resistivity of the liquid under test.

[0005] Electrodes in the prior art and in the present invention are typically made of platinum, gold-plated nickel, titanium, stainless steel, or graphite. The body or manifold of the conductivity / resistivity cell with the flow paths is generally made of a non-conductive material. For example, it can be made of glass or resin. Examples of suitable resins can be selected from the group consisting of, but not limited to, epoxy resin, polyacetal, and polyamide. A preferred polyacetal is polyoxymethylene ("POM").

[0006] The main distinguishing feature between types of conductivity / resistivity cells is the conductivity / resistivity cell's cell constant, identified by the letter K. This cell constant is determined by the size of the electrodes, the distance between the electrodes, and the pattern of the electric field present. Generally, cells with widely spaced, small electrodes will produce a higher voltage, while cells with closely spaced, large electrodes will produce a lower voltage. Measuring conductivity / resistivity requires a transmitter and controller for signal conditioning and a connecting cable to the conductivity / resistivity cell. The system may also include a microprocessor to help automate the conductivity / resistivity measurement process.

[0007] Conductivity is typically measured in millisiemens (mS) or microsiemens (μS). When using contact conductivity electrodes, the geometry of the conductivity cell affects the measured conductivity. To ensure standardization of electrical conductivity measurements, units of specific conductivity are used. Specific conductivity is expressed as millisiemens per centimeter (mS / cm) or microsiemens per centimeter (μS / cm). Resistivity, the reciprocal of conductivity, is typically measured in ohm-meters (Ω m). Specific conductivity = measured conductivity (G) x cell constant (K).

[0008] With a cell constant of 1.0, the measured conductivity (G) is approximately equal to the specific conductivity of the solution. However, a cell constant of 1.0 is not always an appropriate choice. For example, with solutions with very low conductivity, such as pure or ultrapure water, the measuring surfaces of the electrodes must be placed closer together to generate a signal strong enough to reach the controller or conductivity meter. As the path length between the conductive plates decreases, the cell constant also decreases to 0.1 or even 0.01. Conversely, when measuring high-conductivity solutions, a longer path length (higher cell constant) of 10 or 100 will provide more accurate measurements.

[0009] Conductivity / resistivity measurements are important parameters for water purification systems, as they enable control of the purification process and give end users insight into the quality of the water delivered by their water purification products. Depending on the water quality to be measured, an appropriate cell coefficient (K) and electronic hardware must be defined and fine-tuned.

[0010] In a typical water purification system, the typical range of water quality measured is from 5000 μS / cm (concentrated tap water) to 80 megaohms cm (cold ultrapure water). As a result, the range of water impedance measured by the electronics circuitry is a huge 400,000 times.

[0011] To allow this measurement and ensure tolerance, this ratio is reduced by a cell factor. Typically, a cell factor close to 1.0 is used for high conductivity, and a cell factor close to 0.01 is used for high resistivity (low conductivity). The ratio for impedance measured in ohms is reduced from 400,000 to 4,000.

[0012] The cell factor is calculated based on the geometric parameters of the electrodes (diameter, length, gap, orientation, etc.). A cell factor close to 1.0 is likely to be a parallel electrode type, while a cell factor close to 0.01 is likely to be a concentric electrode type. It is extremely difficult, and practically impossible, to create a cell with a factor K=0.01 using parallel electrodes, or a cell with a factor K=1.0 using concentric electrodes.

[0013] Depending on the water quality being measured by the system (ranging from tap water to ultrapure water) and the required flow rate, the cells incorporated into the system can be a combination of parallel and concentric styles with dedicated electronic hardware. From an industrial perspective, interlocking cell geometries and electronics across devices is undesirable because it requires the development of smaller raw materials, multiple assembly processes, and multiple procurement chains. Furthermore, concentric cells can result in excessively high pressure drops, especially at high flow rates.

[0014] A further drawback is that the cell factor is sensitive to variations in the geometry of the machined parts, especially for concentric cells: even small variations due to machining or assembly processes can have a significant effect on the cell factor and therefore the final measurement result. Therefore, the cell factor cannot be determined from the estimated or nominal dimensions of the cell elements, and calibration is required to define the exact cell factor. This calibration is usually performed on a calibration test bench where the water parameters are controlled, and is therefore expensive.

[0015] The problem to be solved is to provide a conductivity / resistivity cell for use in a water purification system for measuring the conductivity / resistivity of a sample liquid, preferably pure or ultrapure water, that can be used regardless of water quality and allows for cell coefficient determination without water calibration. Preferably, such a conductivity / resistivity cell should be manufactured cost-effectively using a simple process and / or be reliable in use. The present invention also provides a water purification system that includes and benefits from the improved conductivity / resistivity cell, and a method for determining the conductivity and / or resistivity of a sample liquid over a flexible range. Summary of the Invention [Problem to be solved by the invention]

[0016] To solve the above problem, the present invention provides a conductivity / resistivity cell having the features of claim 1, a water purification system having the features of claim 11, and a method for determining the conductivity and / or resistivity of a sample liquid having the features of claim 12. Preferred embodiments of the conductivity / resistivity cell and the method are defined in the respective dependent claims.

[0017] The present invention particularly provides a conductivity / resistivity cell comprising: a manifold including a flow path through which a sample liquid to be measured can pass; and a pair of cylindrical electrodes, each having a central longitudinal axis, a diameter d, and an axial end face, the cylindrical electrodes being mounted within the manifold such that the axial end faces of the cylindrical electrodes face each other across a gap disposed a distance e within the flow path, and preferably aligned in the longitudinal direction (X) of the flow path.

[0018] Preferably, the cylindrical electrodes are mounted within the manifold so that their longitudinal central axes are parallel to one another, preferably concentric, and aligned, and preferably perpendicular to the longitudinal direction (X) of the flow channel. Preferably, the manifold is configured so that the axial position of at least one, and preferably both, of the cylindrical electrodes can be adjusted relative to the other to adjust the distance e between the axial end faces of the electrodes facing each other across a gap.

[0019] Preferably, the manifold includes receptacles configured to accommodate electrodes each having a different diameter d. Preferably, the diameter d of the cylindrical electrode is 5 to 30 mm. Preferably, the axial end faces of the cylindrical electrodes are flat, preferably perpendicular to the longitudinal central axis, and more preferably aligned with the longitudinal direction (X) of the flow channel.

[0020] Preferably, the flow channel is dimensioned so that the maximum flow rate of sample liquid through the channel is between 3 l / h and 600 l / h, and the pressure drop at maximum flow rate is 500 mbar or less. Preferably, the cell factor K of the conductivity / resistivity cell is between 0.1 and 1.0, and is preferably adjustable.

[0021] Preferably, the cell coefficient K of the conductivity / resistivity cell is calculated according to the following formula: K=e / (π×d / 2) 2 is determined by e is the distance between the axial end faces of the electrodes across the gap, and d is the diameter of the electrodes.

[0022] Preferably, the diameter d of the cylindrical electrode is 9 to 13 mm, preferably 10 to 12 mm, more preferably 10.5 to 11.5 mm, preferably about 11 mm, and the distance e between the axial end faces of the cylindrical electrodes facing each other across a gap is about 1 mm when the cell factor K is 0.1, and about 10 mm when the cell factor K is 1.0. The present invention provides, inter alia, a water purification system comprising a conductivity / resistivity cell according to the present invention.

[0023] The present invention relates in particular to a method for determining the conductivity and / or resistivity of a sample liquid, comprising the following steps: (a) providing a conductivity / resistivity cell of the present invention; (b) setting a distance e between axial end faces of cylindrical electrodes facing each other across a gap located in the longitudinal direction (X) of the flow channel and preferably aligned therewith; (c) The cell coefficient K is calculated using the following formula: K=e / (π×d / 2) 2 where e is the distance between the axial ends of the electrodes across the gap, and d is the diameter of the electrode; and (d) determining the conductivity and / or resistivity of the sample liquid The method further comprises:

[0024] Preferably, the diameter d of the cylindrical electrode is selected to be 5 to 30 mm, preferably 9 to 13 mm, preferably 10 to 12 mm, more preferably 10.5 to 11.5 mm, preferably about 11 mm, and the distance e between the axial end faces of the cylindrical electrodes facing each other across a gap is set to be about 1 mm to about 10 mm. Preferably, steps (a) and (b) of the method for determining the conductivity and / or resistivity of a sample liquid are carried out during assembly of the conductivity / resistivity cell. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 shows a schematic cross-sectional view of an exemplary conductivity / resistivity cell. [Figure 2] FIG. 2 shows a schematic perspective view of the exemplary conductivity / resistivity cell of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] The conductivity / resistivity cell of the present invention offers the advantage of being able to use the same probes / electrodes and the same manifold regardless of the water quality being measured, which reduces raw material and assembly costs by allowing more of the same parts to be produced / purchased.

[0027] The electrode / probe geometry allows for the determination of the cell factor with only simple dimensional measurements, without the need for water calibration. In some water purification systems, water calibration by the end user is not mandatory, but must be performed at least once to determine the cell factor. The present invention reduces the cost of this task in terms of process cost and capital investment (i.e., no test bench for water calibration is required).

[0028] Tuning the cell factor for next-generation products is easy because it only requires adjusting the gap size and software parameters. The gap dimensions are easily controlled by assembly process parameters that are easy to tweak and verify. The present invention will now be described in detail based on preferred exemplary embodiments with reference to the accompanying exemplary schematic diagrams of FIGS.

[0029] The conductivity / resistivity cell for a water purification system of the present invention will now be described in connection with an exemplary embodiment. It should be noted that the specific design of the exemplary embodiment, particularly the external design, is an example of a particular implementation, but that modifications are possible and within the scope of the present invention, so long as the basic internal functionality defined in the claims is provided.

[0030] The conductivity / resistivity cell 1 according to the exemplary embodiment includes a body or manifold 2 including a flow path 4 through which, in use, a sample liquid to be measured can pass, and a pair of cylindrical electrodes 5, 6 each having a central longitudinal axis 5c, 6c, a diameter d, and preferably flat axial measuring end faces 5b, 6b.

[0031] The body or manifold 2 has connectors 3 at both ends for releasably connecting to supply pipes or hoses (not shown) for introducing or withdrawing the liquid under test into or from the flow paths 4. The connectors 3 thread into corresponding receptacles in the body or manifold 2 and are sealed to the body or manifold 2 by seals 3a, such as O-rings or gaskets (such a threaded connection is shown by way of example on the left side of the manifold). The connectors can also be formed as an integral part of the body or manifold 2, as illustrated by the right side of the manifold, further reducing the number of parts. The connectors 3 can have the same outer diameter but different inner diameters to accommodate pipes or hoses of different diameters / sizes, depending on the rated flow rate of the system in which the cell is used.

[0032] The cylindrical electrodes 5, 6 are mounted in the manifold 2 so that their axial end faces 5b, 6b face each other across a gap 7 located in the flow channel 4, a distance e, i.e., so that the planes of the flat end faces are parallel to each other. The flat axial measuring end faces 5b, 6b are preferably perpendicular to the longitudinal axes 5c, 6c and, more preferably, aligned with the longitudinal direction X of the flow channel 4. The direction of the distance e is therefore perpendicular to the planes of the flat axial end faces 5b, 6b and, preferably, perpendicular to the direction of flow through the section of the flow channel 4, i.e., the longitudinal direction X of the flow channel 4 in which the end faces 5b, 6b are located.

[0033] The cylindrical electrodes 5, 6 are mounted within the manifold 2 so that their central longitudinal axes 5c, 6c are parallel, preferably concentric, or more preferably aligned with each other, and preferably perpendicular to the longitudinal direction X of the flow channel 4 as shown in FIG.

[0034] The manifold 2 is preferably configured so that the axial position of at least one, and preferably both, of the cylindrical electrodes 5, 6 can be adjusted relative to the other to adjust the distance e between the axial end faces 5b, 6b of the electrodes 5, 6 that face each other across the gap 7. Preferably, such adjustment of the distance e occurs during assembly of the conductivity / resistivity cell of the present invention. The distance e remains constant during operation, e.g., throughout the lifetime of the conductivity / resistivity cell. However, if the need arises due to, for example, changes in water purity or requirements, the distance e can also be adjusted later (e.g., after assembly) to accommodate such changing conditions.

[0035] To accommodate electrodes of different diameters within the same body or manifold 2, the manifold 2 may include a receptacle that is larger in diameter than the electrode and an insert or sleeve (not shown) that reduces the difference between the outer periphery of the electrode and the inner periphery of the receptacle.

[0036] The electrodes are sealed to the flow channels 4 by seals 5a, 6a, for example in the form of O-rings or gaskets, or by mechanical deformation of the body or manifold 2 by introducing the electrodes into the body or manifold 2, respectively. If no axial position change is required after initial installation, the electrodes can be fluid-tight sealed and fixed by any suitable mechanical fixing means or shape-setting structures (e.g., protrusions, lashes, or recesses), or by adhesive, or by mechanical deformation of the body or manifold 2 as described above.

[0037] In the exemplary embodiment of the conductivity / resistivity cell 1 shown in FIGS. 1 and 2, the body or manifold 2 is provided with a receptacle or bore 8 into which a thermistor 9 (i.e., resistance thermometer) is inserted and secured (e.g., by a suitable mechanical connection or adhesive) so as to detect the temperature of a sample liquid to be measured passing through the flow path 4 in use. The tip with the measurement cell extends into the flow path 4, and the leads 10 of the thermistor 9 are accessible from outside the manifold 2. The receptacle or bore 8 into which the thermistor 9 is inserted is formed in the body or manifold 2 in the exemplary embodiment, but could also be formed in one of the electrodes 5, 6 (not shown) or in another section of the cell (not shown) attached to the manifold 2.

[0038] The cell factor K of the conductivity / resistivity cell 1 is calculated using the following formula: K=e / (π×d / 2) 2 is determined by The symbol e denotes the distance between the axial end faces 5b and 6b of the electrodes 5 and 6, with the gap 7 sandwiched therebetween, and the symbol d denotes the diameter of the electrodes 5 and 6.

[0039] With respect to the use of the conductivity / resistivity cell 1 in a water purification system, it is preferred that the cell coefficient K of the conductivity / resistivity cell 1 is between 0.1 and 1.0 and can be adjusted by changing only the distance e between the axial end faces 5b, 6b of the electrodes 5, 6 that separate the gap 7.

[0040] Therefore, cells with a cell factor K between 0.1 and 1.0 can use the same electrodes and the same manifold, with the difference being determined by the size of the gap e between the electrodes. That is, the diameter d of electrodes 5 and 6 can be accurately measured before assembling the cell, and the gap e can be measured after assembly. If the dimensions of the manifold section housing the electrodes are known, it may be possible to accurately determine their internal length and gap size simply by measuring the distance the electrodes protrude outside the manifold. The cell factor K can then be calculated using these two measurements, without necessarily having to be verified by measuring water during the calibration process.

[0041] This simple and accurate determination of the cell factor cannot be performed with a concentric cell design because the gap between the electrodes cannot be measured during assembly, and is even more difficult with a parallel cell design because there are three parameters to measure (diameter, length, and axial distance), some of which cannot be measured directly.

[0042] To reduce the cost and size of the cell, the diameter of the electrodes should be as small as possible. For use of the conductivity / resistivity cell 1 in a water purification system, the diameter d of the cylindrical electrodes 5, 6 is preferably between 5 and 30 mm.

[0043] In a preferred embodiment, depending on the combination of the target cell factor and pressure drop limit, the preferred range of diameter d is 9 to 13 mm, preferably 10 to 12 mm, and more preferably 10.5 to 11.5 mm, with the preferred optimum diameter d being 11 mm, and the distance e between the axial end faces 5b, 6b of the cylindrical electrodes 5, 6 facing each other across the gap 7 is approximately 1 mm when the cell factor K is 0.1, and 10 mm when the cell factor K is 1.0. This optimum value will differ for products with different flow rates, different maximum pressure drops, and different cell factors.

[0044] For the use of the conductivity / resistivity cell 1 in a water purification system, it is necessary to consider not only the size of the diameter d and gap e, but also the hydraulic parameters of the flow path, in particular the pressure drop of the liquid to be measured in the cell. Preferably, the flow path 4 is dimensioned so that the maximum flow rate of the sample liquid passing through the flow path 4 is between 3 l / h and 600 l / h, and the pressure drop at the maximum flow rate is 500 mbar or less.

[0045] For the electronic device (controller or meter) connected to the cell's electrodes and evaluating its signal to determine or measure the conductivity / resistivity of the liquid under test, from tap water to ultrapure water, the data acquisition must work with a wide range of equivalent resistors. It is common to use different gain resistors, each dedicated to a specific range. The cell is excited with an AC signal. The frequency of this signal depends on the type of cell and the impedance range to be measured (to take parasitic elements into account). Filtering elements are selected depending on that frequency.

[0046] To accommodate multiple cell coefficients, this approach is modified in accordance with the present invention: multiple gain resistors are still used, but the frequency of the signal depends on the equivalent resistor being measured, and is preferably selected automatically. As known to those skilled in the art, filtering elements are selected to accommodate this frequency range (one gain resistor can be used at multiple frequencies).

[0047] The novel aspect is the ability to measure a wide range of conductivity / resistivity using the same electronic channel, with different cell coefficients depending on the water quality being measured. Since the cell factors are known and recorded in the system memory, related parameters such as frequency and readable range per gain can vary to accommodate different cell factors. This data can be provided and selected through software settings. The required ratio between cell factors can be reduced by using dedicated electronics that can read high equivalent resistance values.

Claims

1. A conductivity / resistivity cell (1) comprising: a manifold (2) including a flow path (4) through which a sample liquid to be measured can pass; a pair of cylindrical electrodes (5, 6) each having a longitudinal central axis (5c, 6c), a diameter d, and axial end faces (5b, 6b); The cylindrical electrodes (5, 6) are mounted in the manifold (2) such that the axial end faces (5b, 6b) of the cylindrical electrodes (5, 6) face each other across a gap (7) disposed at a distance e within the flow path (4) and are preferably aligned in the longitudinal direction (X) of the flow path (4). The conductivity / resistivity cell (1).

2. 2. The conductivity / resistivity cell (1) according to claim 1, wherein the cylindrical electrodes (5, 6) are mounted in the manifold (2) such that their longitudinal central axes (5c, 6c) are parallel to each other, preferably concentric and aligned, and preferably perpendicular to the longitudinal direction (X) of the flow path (4).

3. 3. The conductivity / resistivity cell (1) according to claim 1 or 2, wherein the manifold (2) is configured such that the axial position of at least one, preferably both, of the cylindrical electrodes (5, 6) can be adjusted relative to the other to adjust the distance e between the axial end faces (5 b, 6 b) of the electrodes (5, 6) facing each other across the gap (7).

4. The conductivity / resistivity cell (1) according to any one of claims 1 to 3, wherein the manifold (2) comprises receptacles configured to accommodate electrodes (5, 6) each having a different diameter d.

5. Conductivity / resistivity cell (1) according to any one of claims 1 to 4, wherein the diameter d of the cylindrical electrodes (5, 6) is between 5 and 30 mm.

6. 6. The conductivity / resistivity cell (1) according to any one of claims 1 to 5, wherein the axial end faces (5b, 6b) of the cylindrical electrodes (5, 6) are flat and preferably perpendicular to the longitudinal central axes (5c, 6c), more preferably aligned with the longitudinal direction (X) of the flow channel (4).

7. 7. The conductivity / resistivity cell (1) according to any one of claims 1 to 6, wherein the flow path (4) is dimensioned such that the maximum flow rate of the sample liquid passing through the flow path (4) is between 3 l / h and 600 l / h and the pressure drop at the maximum flow rate is 500 mbar or less.

8. The conductivity / resistivity cell (1) according to any one of claims 1 to 7, wherein the cell factor K of the conductivity / resistivity cell (1) is between 0.1 and 1.0, and is preferably adjustable.

9. The cell coefficient K of the conductivity / resistivity cell (1) is calculated using the following formula: K=e / (π×$ / 2) ２ is determined by e is the distance between the axial end faces (5b, 6b) of the electrodes (5, 6) across the gap (7), and d is the diameter of the electrodes (5, 6). A conductivity / resistivity cell (1) according to claim 8.

10. 10. The conductivity / resistivity cell (1) according to claim 8 or 9, wherein the diameter d of the cylindrical electrodes (5, 6) is 9 to 13 mm, preferably 10 to 12 mm, more preferably 10.5 to 11.5 mm, preferably about 11 mm, and the distance e between the axial end faces (5b, 6b) of the cylindrical electrodes (5, 6) facing each other across the gap (7) is about 1 mm when the cell factor K is 0.1, and about 10 mm when the cell factor K is 1.

0.

11. A water purification system comprising a conductivity / resistivity cell (1) according to any one of claims 1 to 10.

12. 1. A method for determining the conductivity and / or resistivity of a sample liquid, the method comprising the steps of: (a) providing a conductivity / resistivity cell (1) according to any one of claims 1 to 7; (b) setting a distance e between the axial end faces (5b, 6b) of the cylindrical electrodes (5, 6) facing each other across a gap (7) located in the longitudinal direction (X) of the flow channel (4) and preferably aligned therewith; (c) The cell coefficient K is calculated using the following formula: K=e / (π×$ / 2) ２ where e is the distance between the axial end faces (5b, 6b) of the electrodes (5, 6) across the gap (7), and d is the diameter of the electrodes (5, 6); and (d) determining the conductivity and / or resistivity of the sample liquid The method comprising:

13. 13. The method for determining the conductivity and / or resistivity of a sample liquid according to claim 12, wherein the diameter d of the cylindrical electrodes (5, 6) is selected to be between 5 and 30 mm, preferably between 9 and 13 mm, preferably between 10 and 12 mm, more preferably between 10.5 and 11.5 mm, preferably about 11 mm, and the distance e between the axial end faces (5b, 6b) of the cylindrical electrodes (5, 6) facing each other across the gap (7) is set to be between about 1 mm and about 10 mm.

14. 14. A method for determining the conductivity and / or resistivity of a sample liquid according to claim 12 or 13, wherein steps (a) and (b) are carried out during assembly of the conductivity / resistivity cell.

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