Conductance cell system and method for double-range correction

Abstract

The invention discloses a conductance cell system and method for double-range correction, and belongs to the technical field of analytical instruments, the system comprises a first conductance cell and a second conductance cell which are connected in series through a pipeline, and a processing unit connected with the first conductance cell and the second conductance cell. The first conductance cell is suitable for high-concentration detection, and the second conductance cell is suitable for low-concentration detection. The method comprises the following steps: firstly, establishing two calibration curves of different measurement ranges for two conductance cells, and determining critical points of the two curves; during detection, a sample sequentially flows through the two conductance cells, the processing unit selects one of the high-concentration calibration curve and the low-concentration calibration curve for data processing according to a comparison result of a real-time detection signal and a critical point, and finally a concentration value is output. According to the invention, through a series connection structure and intelligent curve selection, the detection range of a single conductance cell is effectively widened, the measurement precision in a full scale is remarkably improved, and automatic and high-precision detection in a wide concentration range is realized.

Description

Technical Field

[0001] This invention belongs to the field of analytical instrument technology, and specifically relates to a dual-range calibration conductivity cell system and method that can automatically switch detection ranges and achieve wide-range high-precision measurement. Background Technology

[0002] Conductivity detection is the most commonly used general-purpose detection method in ion chromatography. Its principle is based on the quantitative relationship between solution conductivity and ion mobility and concentration. According to Kohlrausch's law (Ion Chromatography Methods and Applications (3rd Edition) [M]. Mu Shifen; Zhu Yan; Liu Kena. Chemical Industry Press):

[0003]

[0004] G is the conductance, which is the reciprocal of the resistance (G = 1 / R); A is the cross-sectional area of ​​the electrode; L is the distance between the two electrodes; C i λ represents the ion concentration, in mol / L. i is the limiting molar conductance of the ion.

[0005] The cell constant of a conductivity cell is K = L / A

[0006] conductivity k

[0007]

[0008] When the cell constant is 1, the measured conductivity value is called conductivity. The commonly used unit for conductivity of aqueous solutions is microsiemens per centimeter (μS / cm).

[0009] Electrical conductivity is an important physicochemical parameter for measuring the ability of a solution to conduct electricity, and it is widely used in environmental monitoring, industrial process control, food and beverage, and semiconductor ultrapure water applications. Traditional conductivity measurement systems typically use a single conductivity cell, and their effective measurement range is limited by the cell constant (K value). A single conductivity cell cannot simultaneously achieve both high-sensitivity measurement of low-conductivity solutions (such as ultrapure water) and accurate measurement of high-conductivity solutions (such as concentrated brine).

[0010] To address this issue, existing technologies have developed systems that involve manually switching between different conductivity cells or employing multiple measurement circuits; however, these solutions have significant shortcomings:

[0011] 1. The contradiction between detection range and sensitivity: The dynamic range of a single conductivity cell is limited. If a small electrode area or a large spacing (i.e., adjusting the K value) is designed for measuring high conductivity samples, the detection sensitivity for low conductivity samples will be significantly reduced; conversely, a high-sensitivity conductivity cell suitable for measuring low conductivity is very likely to exceed its range or produce severe electrode polarization effects when measuring high conductivity samples.

[0012] 2. K-value stability issue: The K-value of a conductivity cell is mainly determined by the effective area and spacing of the electrodes. During traditional manufacturing and long-term use, minute mechanical deformations, temperature shocks, or surface contamination can cause slight changes in the electrode spacing, resulting in K-value drift and unreliable measurement data.

[0013] 3. Capacitance effect and electrode polarization: When measuring with DC or low-frequency AC, a double voltage will form at the electrode-solution interface.

[0014] Layer capacitance, especially under conditions of high conductivity or low frequency measurement, can cause polarization effects that lead to significant deviations from the true values ​​in the measured values. Existing solutions, such as switching the measurement frequency or using multi-electrode arrays, can partially alleviate these problems, but they fail to fundamentally resolve the core contradiction of balancing wide measurement range, high accuracy, and high stability.

[0015] Therefore, there is an urgent need for a conductivity measurement system that can cover a wider detection range while ensuring high accuracy and stability in both low and high concentration ranges. Summary of the Invention

[0016] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a dual-range calibrated conductivity cell system and method. This system integrates two conductivity cells with different conductivity constants, and, in conjunction with high-frequency excitation and intelligent algorithms, achieves wide-range, high-precision, and high-stability conductivity measurement.

[0017] To achieve the above objectives, the present invention adopts the following technical solution:

[0018] A dual-range calibrated conductivity cell system, characterized in that it comprises:

[0019] A flow path assembly includes a first conductivity cell and a second conductivity cell, wherein the first conductivity cell has a first detection range and is suitable for high-sensitivity detection;

[0020] A second conductivity cell has a second detection range and is suitable for low-sensitivity detection, wherein the first and second detection ranges together cover a continuous conductivity range.

[0021] The first conductivity cell and the second conductivity cell are connected in series through a pipeline, so that the sample can flow through the first conductivity cell and the second conductivity cell in sequence;

[0022] The excitation module includes a high-frequency AC excitation source for applying high-frequency AC current to the electrodes of the first and second conductivity cells to suppress electrode polarization effects.

[0023] The temperature control module includes a heating element, which is disposed inside the system housing or in thermal contact with the measuring unit to maintain a constant measuring temperature.

[0024] A control and processing unit configured to perform the following steps:

[0025] a) Control the first and second conductivity cells to measure a series of standard solutions and acquire response data respectively;

[0026] b) Based on the response data of the first conductivity cell, establish a first conductivity / concentration-response relationship model; based on the response data of the second conductivity cell, establish a second conductivity / concentration-response relationship model.

[0027] c) Determine the overlapping region between the first conductivity / concentration-response relationship model and the second conductivity / concentration-response relationship model, and define specific values ​​within this overlapping region as critical points (or critical regions) used to distinguish sample detection paths;

[0028] d) Obtain the preliminary response of the unknown sample, and based on the critical point, automatically select the first conductivity / concentration-response relationship model or the second conductivity / concentration-response relationship model to accurately calibrate and calculate the unknown sample.

[0029] Furthermore, the distance between the electrodes of the first and second conductivity cells is fixed and controlled by a precision mechanical structure so that the first and second conductivity cells have stable and different conductivity cell constants (K values).

[0030] Furthermore, the electrode spacing of the first conductivity cell is set to be smaller than that of the second conductivity cell, so that the first conductivity cell has a smaller conductivity cell constant, which is suitable for the detection of samples with low conductivity (high sensitivity), while the second conductivity cell has a larger conductivity cell constant, which is suitable for the detection of samples with high conductivity (low sensitivity).

[0031] Furthermore, the AC frequency applied by the high-frequency AC excitation source is in the range of 10kHz to 100kHz. The excitation module is configured to perform time-division excitation or synchronous isolation excitation on the first and second conductivity cells to suppress electrical interference between channels.

[0032] Furthermore, both the first conductivity / concentration-response relationship model and the second conductivity / concentration-response relationship model are linear equations.

[0033] Furthermore, the overlapping region is the two linear equations R 2 Region ≥0.999. The critical point is the average of the sum of the lowest point in the high-concentration overlap region and the highest point in the low-concentration overlap region.

[0034] Furthermore, the heating tube is an annular tube surrounding the measuring flow path or a U-shaped tube embedded in the system housing, with a heating wire disposed inside. Preferably, the heating module includes independent first and second heating tubes, respectively corresponding to the first and second conductivity cells, providing independent temperature control.

[0035] Furthermore, the precision mechanical structure includes a conductivity cell cavity made of rigid material, and the electrode is precisely positioned and fixed within the cavity.

[0036] Furthermore, the first conductivity cell and the second conductivity cell are integrated and packaged in the same modular unit.

[0037] A method for measuring the conductivity of the dual-range calibrated conductivity cell system is also provided:

[0038] S1. Perform system calibration steps: Establish first and second conductivity / concentration-response relationship models by measuring a series of standard solutions, and determine the critical region and critical point;

[0039] S2. Sample measurement and judgment steps: Obtain preliminary information of the sample to be tested and compare it with the critical point;

[0040] S3. Channel Selection and Precise Measurement Steps: Based on the comparison results, the sample to be tested is calibrated using either the first conductivity / concentration-response relationship model or the second conductivity / concentration-response relationship model.

[0041] The beneficial effects of this invention are as follows:

[0042] 1. Wide dynamic range: With two conductivity cells dedicated to different ranges, the system can cover an extremely wide conductivity measurement range, from ultrapure water to high-concentration electrolytes.

[0043] 2. High precision and high sensitivity: Each conductivity cell operates within its optimal linear response range, avoiding nonlinear errors of a single conductivity cell under extreme ranges.

[0044] 3. Seamless switching: Through dual-range full scan and critical point algorithm, accurate correlation and smooth transition of data from two detection ranges are achieved, eliminating the jump error that may be caused by traditional switching.

[0045] 4. Stable structure: The use of a precision mechanical structure to fix the electrode spacing, combined with high-frequency excitation, effectively solves the problems of K-value drift and electrode polarization, thus improving the reliability and repeatability of the system. Attached Figure Description

[0046] Figure 1 This is a flowchart of a conductivity cell method with dual-range calibration according to the present invention;

[0047] Figure 2 This is a schematic diagram of a specific implementation of the dual conductivity cell unit in Embodiment 1 of the present invention;

[0048] Figure 3 This is a partially enlarged cross-sectional view of the structural schematic diagram of the dual conductivity cell unit in Embodiment 1 of the present invention;

[0049] Figure 4 This is a schematic diagram of the fixing clamp structure of the dual conductivity cell unit in Embodiment 1 of the present invention;

[0050] Figure 5 This is a schematic diagram of the conductivity cell cavity of the dual conductivity cell unit in Embodiment 1 of the present invention;

[0051] Figure 6 This is a schematic diagram of a specific implementation of the dual conductivity cell unit in Embodiment 2 of the present invention;

[0052] Figure 7 This is a partially enlarged cross-sectional view of the structural schematic diagram of the dual conductivity cell unit in Embodiment 2 of the present invention;

[0053] Figure 8 This is a schematic diagram of the fixing device structure of the dual conductivity cell unit in Embodiment 2 of the present invention;

[0054] Figure 9 This is a schematic diagram of the conductivity cell cavity of the dual conductivity cell unit in Embodiment 2 of the present invention.

[0055] Figure 10 These are two conductivity / concentration-response relationship models established by dual-range calibration in Embodiment 1 of the present invention, which show the response curves of high-sensitivity and low-sensitivity conductivity cells and their overlapping critical points.

[0056] Among them, 1-first conductivity cell, 2-second conductivity cell, 3-conductivity cell cavity, 4-first heating tube, 5-second heating tube, 6-first conductivity cell fixing clip, 7-second conductivity cell fixing clip, 6-1-first conductivity cell fixing buckle, 7-1-second conductivity cell fixing buckle Detailed Implementation

[0057] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Conductivity and concentration have a linear relationship. This embodiment uses concentration as an example for illustration.

[0058] Example 1

[0059] like Figure 2As shown, the dual-range calibrated conductivity cell system of this embodiment includes a first conductivity cell and a second conductivity cell. The first conductivity cell has a first detection range of 0.05 to 1.5 ppm, which is suitable for high-sensitivity detection. The second conductivity cell has a second detection range of 1 to 30 ppm, which is suitable for low-sensitivity detection. The first detection range and the second detection range together cover the conductivity range of 0.05 to 30 ppm.

[0060] The first conductivity cell and the second conductivity cell are connected in series through a pipeline, and the sample can flow through the first conductivity cell and the second conductivity cell in sequence.

[0061] A high-frequency AC excitation source is used to apply a 50kHz high-frequency AC current to the electrodes of the first and second conductivity cells.

[0062] A heating module includes a heating tube disposed inside a conductivity cell cavity, including a first heating tube and a second heating tube. The first heating tube is disposed corresponding to a first conductivity cell and the second heating tube is disposed corresponding to a second conductivity cell, providing independent temperature control for the first conductivity cell and the second conductivity cell, respectively.

[0063] A control and processing unit, configured as follows:

[0064] a) Control the high-sensitivity conductivity cell and the low-sensitivity conductivity cell to measure the standard solutions in the range of 0.05 to 30 ppm, and obtain response data A and B;

[0065] b) Based on the response data A of the high-sensitivity conductivity cell, establish a first conductivity / concentration-response relationship model;

[0066] c) Based on the response data B of the low-sensitivity conductivity cell, establish a second conductivity / concentration-response relationship model;

[0067] d) Determine the overlapping area between the first relation model and the second relation model, and define the overlapping area as the overlapping area used to distinguish sample detection paths. Calculate the critical point value in the overlapping area, and define the value point as the critical point used to distinguish sample detection paths.

[0068] e) Based on the critical point, automatically select the high-sensitivity conductivity cell or the low-sensitivity conductivity cell to perform measurement calculations on the unknown sample.

[0069] like Figure 3 As shown, the electrode spacing d1 of the first conductivity cell is set to be smaller than the electrode spacing d2 of the second conductivity cell, so that the first conductivity cell has a smaller cell constant, suitable for the detection of low conductivity (high sensitivity) samples, while the second conductivity cell has a larger cell constant, suitable for the detection of high conductivity (low sensitivity) samples. Figure 4 , 5 As shown, the first and second conductivity cells are securely mounted in the conductivity cell cavity using a π-shaped fixing clip. Specifically, the cavity has a space inside to accommodate the fixing clip, and two through holes at the bottom of the cavity for the two vertical legs of the fixing clip to pass through. By inserting the legs of the fixing clip into the through holes, the conductivity cells are precisely positioned and firmly fixed in a predetermined position within the cavity.

[0070] like Figure 10 As shown, two conductivity / concentration-response relationship models are presented, illustrating the response curves of high-sensitivity and low-sensitivity conductivity cells and their overlapping critical points.

[0071] Example 2

[0072] like Figure 6 As shown, the dual-range calibrated conductivity cell system of this embodiment includes a first conductivity cell and a second conductivity cell. The first conductivity cell has a first detection range of 0.05 to 1.5 ppm, which is suitable for high-sensitivity detection. The second conductivity cell has a second detection range of 1 to 30 ppm, which is suitable for low-sensitivity detection. The first detection range and the second detection range together cover the conductivity range of 1 to 1.5 ppm.

[0073] The first conductivity cell and the second conductivity cell are connected in series through a pipeline, and the sample can flow through the first conductivity cell and the second conductivity cell in sequence.

[0074] A high-frequency AC excitation source is used to apply a 50kHz high-frequency AC current to the electrodes of the first and second conductivity cells.

[0075] A heating module includes a heating tube disposed inside the conductivity cell cavity;

[0076] A control and processing unit, configured as follows:

[0077] a) Control the high-sensitivity conductivity cell and the low-sensitivity conductivity cell to measure the standard solutions in the range of 0.05 to 30 ppm, and obtain response data A and B;

[0078] b) Based on the response data A of the high-sensitivity conductivity cell, establish a first conductivity / concentration-response relationship model;

[0079] c) Based on the response data B of the low-sensitivity conductivity cell, establish a second conductivity / concentration-response relationship model;

[0080] d) Determine the overlapping area between the first relational model and the second relational model and calculate the critical point value, and define the value point as the critical point used to distinguish the sample detection path;

[0081] e) Based on the critical point, automatically select the high-sensitivity conductivity cell or the low-sensitivity conductivity cell to measure the unknown sample.

[0082] like Figure 7 As shown, the electrode spacing d1 of the first conductivity cell is set to be smaller than the electrode spacing d2 of the second conductivity cell, so that the first conductivity cell has a smaller conductivity cell constant and is suitable for the detection of low conductivity (high sensitivity) samples, while the second conductivity cell has a larger conductivity cell constant and is suitable for the detection of high conductivity (low sensitivity) samples.

[0083] like Figure 8 , 9 As shown, the conductivity cell is secured by an arched snap-on cap structure. This structure includes an arched snap-on cap that conforms to the shape of the conductivity cell electrode, and screw mounting holes located on the conductivity cell cavity. The arched snap-on cap covers the electrode, creating a uniform downward pressure on the electrode. A screw is then inserted through the snap-on cap and into the screw holes in the cavity, thereby firmly pressing and securing the electrode in its predetermined mounting position.

[0084] like Figure 10 As shown, two conductivity / concentration-response relationship models are presented, illustrating the response curves of high-sensitivity and low-sensitivity conductivity cells and their overlapping critical points.

[0085] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A conductivity cell system with dual-range calibration, characterized in that, include: A flow path assembly includes a first conductivity cell and a second conductivity cell connected in series via a pipeline, allowing the fluid to be measured to flow sequentially through the first conductivity cell and the second conductivity cell; wherein, the first conductivity cell is configured with a first conductivity cell constant, suitable for detecting a first conductivity range; the second conductivity cell is configured with a second conductivity cell constant, suitable for detecting a second conductivity range; the lower limit of the first conductivity range is lower than the lower limit of the second conductivity range, and the two partially overlap to cover a continuous conductivity detection interval; The excitation module includes a high-frequency AC excitation source, configured to apply a high-frequency AC excitation signal to the electrodes of the first conductivity cell and the second conductivity cell; The temperature control module includes a heating unit disposed inside the system housing or in thermal contact with the first conductivity cell and the second conductivity cell; The control and processing unit, connected to the excitation module, temperature control module, and conductivity cell signal output terminal, is configured to perform the following operations: a) The control system measures a series of standard solutions with known concentration values ​​to obtain the first response data of the first conductivity cell and the second response data of the second conductivity cell, respectively; b) Based on the first response data, establish a first conductivity / concentration-response relationship model, and based on the second response data, establish a second conductivity / concentration-response relationship model; c) Determine the boundary region between the first conductivity / concentration-response relationship model and the second conductivity / concentration-response relationship model, and establish a range switching strategy; d) Obtain the estimated response value of the unknown sample, and calculate the conductivity of the unknown sample by selecting either the first conductivity / concentration-response relationship model or the second conductivity / concentration-response relationship model based on the comparison result between the estimated response value and the range switching critical point.

2. The dual-range calibrated conductivity cell system according to claim 1, characterized in that, The distance between the electrodes of the first and second conductivity cells is fixed and controlled by a precision mechanical structure so that the first and second conductivity cells have stable and different conductivity cell constants (K values).

3. The dual-range calibrated conductivity cell system according to claim 2, characterized in that, The electrode spacing of the first conductivity cell is different from that of the second conductivity cell, which makes the first conductivity cell have a smaller cell constant and is suitable for the detection of low conductivity samples (high sensitivity mode); while the second conductivity cell has a larger cell constant and is suitable for the detection of high conductivity samples (low sensitivity mode).

4. The dual-range calibrated conductivity cell system according to claim 1, characterized in that, The AC frequency applied by the high-frequency AC excitation source is in the range of 10kHz to 100kHz, and the excitation module is configured to perform time-division excitation or synchronous isolation excitation on the first conductivity cell and the second conductivity cell to suppress electrical interference between channels.

5. The dual-range calibrated conductivity cell system according to claim 1, characterized in that, Both the first conductivity / concentration-response relationship model and the second conductivity / concentration-response relationship model are linear regression equations.

6. The dual-range calibrated conductivity cell system according to claim 5, characterized in that, The range switching critical point is the conductivity or concentration value corresponding to the average of the sum of the lowest point of the high-concentration overlap region and the highest point of the low-concentration overlap region of the two linear regression equations.

7. The dual-range calibrated conductivity cell system according to claim 1, characterized in that, The heating tube is an annular tube surrounding the measurement flow path or a U-shaped tube embedded in the system housing, and an electric heating wire is provided inside the heating tube.

8. The dual-range calibrated conductivity cell system according to claim 7, characterized in that, The heating unit includes a first heating tube and a second heating tube that are independent of each other. The first heating tube is set to correspond to the first conductivity cell, and the second heating tube is set to correspond to the second conductivity cell, so as to provide independent temperature control for the first conductivity cell and the second conductivity cell respectively.

9. The dual-range calibrated conductivity cell system according to claim 2, characterized in that, The precision mechanical structure includes a conductivity cell cavity made of rigid material, and the electrodes are precisely positioned and embedded in the cavity to prevent relative displacement.

10. The dual-range calibrated conductivity cell system according to claim 1, characterized in that, The first and second conductivity cells are integrated and packaged in the same modular unit to form an integrated dual-channel conductivity cell.

11. A method for measuring the conductivity of a conductivity cell system based on the dual-range calibration described in any one of claims 1-10, characterized in that, Includes the following steps: S1. System calibration steps: sequentially introduce a series of standard solutions, record the response signals of the first conductivity cell and the second conductivity cell respectively, construct the first conductivity / concentration-response relationship model and the second conductivity / concentration-response relationship model, and obtain the range overlap area of ​​the two models to determine the range switching critical point; S2. Sample Initial Measurement and Judgment Steps: Measure the preliminary response signal of the sample to be tested, and compare the preliminary response signal or the preliminary conductivity value based on its conversion with the range switching critical point. S3. Model selection and calculation steps: If the comparison results show that the sample is within the first conductivity range, then call the first conductivity / concentration-response relationship model to calculate the final result; If the sample is within the second conductivity range, the second conductivity / concentration-response relationship model is invoked to calculate the final result.

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