A planar seven-electrode conductivity sensor

Abstract

The present application relates to the technical field of solution conductivity measurement, and particularly relates to a planar seven-electrode conductivity sensor, which comprises a ceramic substrate, and left outer electrodes, left middle electrodes, left inner electrodes, a center electrode, right inner electrodes, right middle electrodes and right outer electrodes which are sequentially and parallelly distributed on the ceramic substrate from left to right, wherein the middle electrodes and the left outer electrodes and the right outer electrodes form excitation current electrodes, the left middle electrodes, the left inner electrodes, the right inner electrodes and the right middle electrodes form voltage test electrodes, the size of the excitation current electrodes is slightly larger than that of the voltage test electrodes, and the front end surface of the middle electrodes is enlarged, so that the electric field distribution can be optimized and the polarization effect can be reduced. Meanwhile, the back end of the electrodes is designed to be bent to form a local electric field closed loop, so that the electric field strength is enhanced and the influence of the adjacent effect is reduced. In addition, the sensor is designed to be miniaturized, has low power consumption, strong anti-pollution ability and other characteristics, so that it has a wide range of applications in various applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solution conductivity measurement, and particularly relates to a planar seven-electrode conductivity sensor. BACKGROUND

[0002] The conductivity sensor is a sensitive element for detecting the change of solution resistance, and is widely used in human production and life. It is an indispensable detection and monitoring device in the production and technical development of electric power, chemical industry, environmental protection, food, semiconductor industry, marine research and development, and is particularly important in monitoring and analyzing the conductivity of water, including industrial water, domestic water, seawater characteristics, and the measurement and monitoring of battery electrolyte properties.

[0003] The conductivity sensor can be mainly divided into electrode conductivity sensor and electromagnetic conductivity sensor according to the working principle. The electrode conductivity sensor is mainly divided into three-electrode, four-electrode and seven-electrode three types, and is widely concerned due to the advantages of fast response speed and high precision. Among them, the seven-electrode conductivity sensor has the highest precision.

[0004] With the increasing demand for accurate data in marine science, environmental monitoring and industrial automation, the high efficiency, low cost and easy maintenance of the sensor will make it the first choice in these fields. Chinese patent CN113495191B discloses a seven-electrode conductivity sensor, which is composed of a ceramic material made of a cylindrical conductivity cell and seven parallel distributed metal ring inner electrodes distributed on the inner wall of the ceramic cylindrical conductivity cell. The processing process is relatively complex, and since the tubular structure is adopted, it is not convenient to clean, which reduces the long-term stability and reliability. SUMMARY

[0005] To solve the above problems, the present application provides a planar seven-electrode conductivity sensor, which adopts a planar structure design and realizes accurate measurement of solution conductivity through its unique electrode structure.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A planar seven-electrode conductivity sensor, comprising a ceramic substrate, and a left outer electrode, a left middle electrode, a left inner electrode, a center electrode, a right inner electrode, a right middle electrode and a right outer electrode which are parallel distributed on the ceramic substrate from left to right, the middle electrode and the left outer electrode and the right outer electrode form excitation current electrodes, the left middle electrode, the left inner electrode, the right inner electrode and the right middle electrode form voltage test electrodes, the width of the excitation current electrode is slightly larger than that of the voltage test electrode, and the front end face of the middle electrode is enlarged, which is conducive to reducing the current distribution density in the electrode and further weakening the polarization effect.

[0008] Further, the rear ends of the left outer electrode, the left middle electrode, the left inner electrode, the right inner electrode, the right middle electrode and the right outer electrode are all designed to be bent, forming a local closed loop of electric field, which helps to concentrate the electric field force lines and enhance the sensitivity of the sensor to solution changes.

[0009] Further, the bent sections of the left outer electrode and the right outer electrode are symmetrically arranged, the bent sections of the left middle electrode and the right middle electrode are symmetrically arranged, and the bent sections of the left inner electrode and the right inner electrode are symmetrically arranged.

[0010] Further, the straight sections of the left outer electrode, the left middle electrode and the left inner electrode are shortened in sequence from left to right.

[0011] Further, the straight sections of the right outer electrode, the right middle electrode and the right inner electrode are shortened in sequence from left to right.

[0012] Further, the lengths of the bent sections of the left outer electrode, the left middle electrode and the left inner electrode are shortened in sequence from outside to inside, and the lengths of the bent sections of the right outer electrode, the right middle electrode and the right inner electrode are shortened in sequence from outside to inside.

[0013] The present application adopts a unique seven-electrode configuration, in which the central and two-side excitation electrodes are slightly wider than the voltage test electrodes, the central excitation electrode has a larger front end area, the electric field distribution is optimized, and the polarization effect is reduced. The bent design of the rear end of the electrode can form a local electric field closed loop, enhance the electric field strength, and reduce the influence of the adjacent effect. In addition, the sensor design considers miniaturization, has low power consumption, strong anti-pollution ability and other characteristics, so that it has a wide range of applications in various applications.

[0014] Compared with the design of the circular tube type conductivity cell, the planar conductivity cell design has the advantages of large flow guiding space, small fluid resistance and low power consumption and heat during measurement. In addition, the open seven-electrode conductivity cell has the advantage of super microstructure after the MEMS process, which not only is easy to clean and can prevent microorganisms from adhering in seawater, but also can integrate the conductivity and temperature sensors, without the need for additional underwater pump assistance, and is particularly suitable for ocean measurement fields such as towed and fast profile measurement. BRIEF DESCRIPTION OF DRAWINGS

[0015] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0016] Figure 1 It is a schematic diagram of a planar strip-shaped seven-electrode sensor.

[0017] Figure 2 It is an approximate structure potential diagram of the strip-shaped electrode.

[0018] Figure 3 The size diagram of the planar special pattern seven-electrode sensor.

[0019] Figure 4 The simulation potential distribution and field intensity distribution diagram when the planar seven-electrode sensor adopts strip electrodes.

[0020] Figure 5 The simulation potential distribution and field intensity distribution diagram when the planar seven-electrode sensor adopts the design of increasing the whole area of the excitation electrode.

[0021] Figure 6 The simulation potential distribution and field intensity distribution diagram when the planar seven-electrode sensor adopts the design of increasing the area of the front end of the excitation electrode.

[0022] Figure 7 The simulation potential distribution and field intensity distribution diagram when the ground electrode of the planar seven-electrode sensor is partially closed.

[0023] Figure 8 The simulation potential distribution and field intensity distribution diagram when the sensor adopts ring electrodes.

[0024] Figure 9 The size diagram of the sensor adopting ring electrodes. DETAILED DESCRIPTION

[0025] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application.

[0026] As shown in Figure 1 A planar seven-electrode conductivity sensor of the present application, comprising a ceramic substrate, and a left outer electrode, a left middle electrode, a left inner electrode, a center electrode, a right inner electrode, a right middle electrode, and a right outer electrode distributed in parallel on the ceramic substrate from left to right, the middle electrode and the left outer electrode and the right outer electrode form an excitation current electrode, the left middle electrode, the left inner electrode, the right inner electrode, and the right middle electrode form a voltage test electrode, the width of the excitation current electrode is slightly larger than that of the voltage test electrode, and the front end face of the middle electrode is enlarged, with a large front end area, which optimizes the electric field distribution and reduces the polarization effect, in particular:

[0027] When measuring circuits using AC power, electrode polarization is usually mild. However, when measuring high-concentration solutions, polarization can be significantly amplified if the current density applied to the electrode is too high or if the power supply voltage contains a DC component. This type of polarization is primarily triggered by the formation of the electric double layer on the electrode surface or changes in electrolyte concentration near the electrode during electrolysis. The former, known as chemical polarization, involves a "galvanic cell" effect where electrolysis products create a reverse potential difference between the electrode and the solution, leading to a decrease in current and an increase in equivalent solution resistance, thus affecting measurement accuracy. The latter, concentration polarization, occurs when electrolysis causes a rapid decrease in the ion concentration of the solution near the electrode. The ion supply rate from the solution fails to keep up with the ion consumption rate at the electrode, resulting in an imbalance at the electrode-solution contact surface, which interferes with the accurate measurement of solution concentration.

[0028] Based on electrochemical theory, the error ΔR caused by polarization can be deduced, that is:

[0029]

[0030] In the formula, U is the polarization potential in V; f is the frequency of the power supply in Hz; R s The solution resistance between the electrodes, in Ω / cm 2 .

[0031] The electrode polarization error ΔR is directly proportional to the square of the electrode polarization potential, inversely proportional to the square of the solution resistance, and inversely proportional to the power supply frequency.

[0032] According to the empirical formula proposed by Tafel in 1905:

[0033] U = a + blog|J(r)|

[0034] In the formula, a and b are called Tafel constants, and a represents the current density in unit values ​​(1 A / cm²). 2 The overpotential value at which the electrode material is applied is related to factors such as the properties of the electrode material, the state of the electrode surface, the composition of the solution, and the temperature.

[0035] J(r) is the current density at the electrode surface, A / cm². 2 .

[0036] The expression for the current density on the electrode surface is:

[0037]

[0038] In the formula, I is the current intensity (A); S is the electrode surface area (cm²). 2 .

[0039] Therefore, increasing the surface area of the electrode can reduce the current density, thereby reducing the polarization potential U, which has a significant effect on reducing the polarization error ΔR. Therefore, when designing and manufacturing electrodes, the surface area of the electrode in contact with the solution should be increased as much as possible under the conditions permitted.

[0040] When the current passes through the solution, the solution resistance calculation formula is:

[0041]

[0042] In the formula, L is the conductive length of the electrolyte solution (related to the electrode spacing), cm;

[0043] A is the conductive cross-sectional area of the electrolyte solution (related to the electrode area), cm 2 ;

[0044] ρ is the resistivity, Ω / cm 2 .

[0045] The conductivity σ calculation formula is:

[0046]

[0047] Let the conductivity constant K be:

[0048]

[0049] Therefore, the expression of the solution resistance is:

[0050]

[0051] Substituting the K value calculation formula can be obtained:

[0052]

[0053] When the conductivity cell constant K decreases, the polarization error will increase, so it is necessary to avoid the decrease of the conductivity cell constant as much as possible.

[0054] In the constant calculation of the seven-electrode open conductivity cell, when considering the use of one excitation electrode 1 and two ground electrodes 4, 7, the three electrodes are regarded as three approximate hemispheres, each with a radius of a, and the distance between them is d, as shown in Figure 1 and Figure 2 Under this configuration, when d is much larger than a, the calculation method of the conductivity cell will be more effective. In this scenario, we assume that the conductivity of seawater is σ, and the seawater is regarded as a semi-infinite space. By applying an excitation signal of an alternating current source through the three electrodes, a potential difference will be generated between the electrodes, and an electric field E(r) will be formed, where the current source density J(r) of the current source at any point is purely radial.

[0055] According to the electric field theory,

[0056]

[0057] Where r is the radius of the current source, the electric field E(r) can be expressed as:

[0058]

[0059] The potential φ generated by the three superimposed current sources can be expressed as:

[0060]

[0061] r1, r2, r $ The approximate potential difference ΔV between the two hemispherical electrodes can be obtained as:

[0062]

[0063] According to Ohm's law, we have:

[0064]

[0065] The approximate open-conductance cell constant calculation result is obtained:

[0066]

[0067] Since d>>a, the expression of K is approximated as:

[0068]

[0069] When the radius of the excitation electrode is larger, the surface area of the electrode is larger, and the conductance cell constant is smaller.

[0070] Therefore, the present application takes into account the polarization potential and the conductance cell constant, expands the front end area of the central excitation electrode, significantly reduces the electrode surface current density, while keeping the remaining part of the excitation electrode area in an elongated state, so as to minimize the polarization error of the sensor.

[0071] In order to form a local electric field closed loop, enhance the electric field strength, and reduce the influence of the adjacent effect, the rear ends of the left outer electrode, the left middle electrode, the left inner electrode, the right inner electrode, the right middle electrode, and the right outer electrode are designed to be bent, and the bent sections of the left outer electrode and the right outer electrode are symmetrically arranged, the bent sections of the left middle electrode and the right middle electrode are symmetrically arranged, and the bent sections of the left inner electrode and the right inner electrode are symmetrically arranged.

[0072] The electric field generated by a planar seven-electrode sensor is distributed over a relatively large area. Therefore, if any insulating or conductive object enters the electric field, the cell constant will change; this is known as the proximity effect. The proximity effect can usually be reduced by limiting the range of the electric field measured by the conductivity cell.

[0073] To ensure that the electric field is mainly concentrated near the sensor area, the open-type conductive cell of this invention is fabricated using microchip technology and implemented by designing electrodes with a specific pattern. In this embodiment, the electrodes with the specific pattern meet the following conditions: (1) the middle electrode and the outermost electrode are slightly wider than the other electrodes, ranging from 4 to 6 times the width of the other electrodes; (2) the front end of the middle electrode has a square area, with a side length ranging from 9 to 11 times the width of the rear end of the middle electrode; (3) all corners are rounded, with a rounded angle of 90 degrees; (4) the tip of the rear end of the electrode has a rounded corner of 180 degrees; (5) the length of the bends decreases sequentially from the outside to the inside; (6) the length of the straight segments ensures that the rounded corners of the rear end of the electrode are approximately on the extension of the diagonal of the square. This design strategy aims to confine the vast majority of the electric field to the area adjacent to the conductive cell, thereby minimizing the impact of proximity effects. In this way, even if an insulator or conductor is close to the conductive cell, the electric field distribution will not be significantly affected, thus effectively reducing the interference of external contamination on conductivity measurement and ensuring the reliability of the measurement results.

[0074] like Figure 3 As shown, in a preferred embodiment of the present invention, the distance between the left outer electrode, left middle electrode, left inner electrode, middle electrode, right inner electrode, right middle electrode, and right outer electrode is 0.4 mm. The rear ends of the left outer electrode, left middle electrode, left inner electrode, right inner electrode, right middle electrode, and right outer electrode are designed with a bend, and all turning points are rounded with a rounded corner angle of 90 degrees. The width of the left outer electrode is 0.10 mm, the upper rounded corner radius is 0.14 mm, the lower rounded corner radius is 0.35 mm, and the length of the straight segment is 0.16 mm. The width of the left middle electrode is 0.02 mm, the upper rounded corner radius is 0.16 mm, and the lower rounded corner radius is 0. The width of the left inner electrode is 0.02mm, the upper fillet radius is 0.16mm, the lower fillet radius is 0.26mm, and the length of the straight segment is 0.73mm. The width of the middle electrode is 0.10mm, the front end enlarged area is rectangular with a width of 1mm, and its fillet radius is 0.15mm. The width, upper fillet radius, lower fillet radius, and length of the straight segment of the right inner electrode are the same as those of the left inner electrode. The width, upper fillet radius, lower fillet radius, and length of the straight segment of the right middle electrode are the same as those of the left middle electrode. The width, upper fillet radius, lower fillet radius, and length of the straight segment of the right outer electrode are the same as those of the left outer electrode.

[0075] according to Figures 4-8 In seawater conductivity measurements, strip electrode designs cause a significant portion of the electric field to diffuse outside the conductivity cell. This configuration makes the measurement performance susceptible to changes in the electric field distribution. Especially when a conductive object passes near the conductivity cell, this external influence can interfere with the measurement results, leading to decreased accuracy. In contrast, arc-shaped electrodes (such as...) Figures 8-9 As shown, the central disc is the excitation electrode, the outermost ring is the grounding electrode, and the two middle rings are the voltage electrodes (all dimensions are in mm). This ingenious design confines the electric field within the conductivity cell, avoiding the presence of external current. This means that even if objects move or are present outside the conductivity cell, the constant of the conductivity cell is minimally affected. This design effectively eliminates the proximity effect. Through precise control of the internal electric field, the arc-shaped electrode design ensures that conductivity measurements are less affected by changes in external conditions, thus providing consistent measurement results under various environmental conditions. In contrast, the electric field distribution of the ring-shaped electrode has defects; the electric field is too concentrated near the excitation electrode. When the voltage electrode is tested in seawater, the measured voltage is relatively small, causing a significant error.

[0076] Therefore, this invention incorporates a bend design at the rear end of the grounding electrode, optimizing the electric field distribution and achieving local closed-loop control. This further confines the electric field within the test area, and the voltage electrode can perform conductivity testing in areas with high field strength. This reduces the proximity effect, enhances the sensor's anti-interference capability, and maintains high measurement sensitivity even under interference conditions.

[0077] The open-type seven-electrode conductivity cell of this invention is fabricated using MEMS technology and has the advantages of an ultra-microstructure. It is not only easy to clean and can prevent the adhesion of microorganisms in seawater, but also integrates conductivity and temperature sensors into one unit. It does not require the addition of an underwater pump, making it particularly suitable for marine measurement fields such as towed and rapid profiling measurements.

[0078] Compared to tubular conductivity cell designs, planar conductivity cell designs offer advantages such as larger flow space, lower fluid resistance, and lower power consumption and heat generation during measurement. Furthermore, compared to tubular electrode sensors, the planar structure of the planar seven-electrode sensor results in lower manufacturing costs and facilitates mass production. The planar design also aids in sensor cleaning and maintenance, particularly in corrosive and polluting environments like seawater, making it easier to remove dirt and deposits. These characteristics significantly improve the long-term stability and reliability of planar seven-electrode sensors compared to traditional tubular sensors.

[0079] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essence of the present application.

Claims

1. A planar seven-electrode conductivity sensor, characterized by: The application relates to a ceramic substrate and left outer electrodes, left middle electrodes, left inner electrodes, a center electrode, right inner electrodes, right middle electrodes and right outer electrodes which are arranged in parallel on the ceramic substrate from left to right, the middle electrodes and the left outer electrodes and the right outer electrodes form excitation current electrodes, the left middle electrodes, the left inner electrodes, the right inner electrodes and the right middle electrodes form voltage test electrodes, the width of the excitation current electrodes is larger than that of the voltage test electrodes, and the front end surface of the middle electrodes is enlarged. The rear ends of the left outer electrodes, the left middle electrodes, the left inner electrodes, the right inner electrodes, the right middle electrodes and the right outer electrodes are designed to be bent to form a local closed loop of electric field. The bent sections of the left outer electrodes and the right outer electrodes are symmetrically arranged, the bent sections of the left middle electrodes and the right middle electrodes are symmetrically arranged, and the bent sections of the left inner electrodes and the right inner electrodes are symmetrically arranged.

2. A planar seven-electrode conductivity sensor as claimed in claim 1, characterized in that: The straight sections of the left outer electrodes, the left middle electrodes and the left inner electrodes are shortened from left to right.

3. A planar seven-electrode conductivity sensor as claimed in claim 1, characterized in that: The straight sections of the right outer electrodes, the right middle electrodes and the right inner electrodes are shortened from left to right.

4. A planar seven-electrode conductivity sensor as claimed in claim 1, characterized in that: The lengths of the bent sections of the left outer electrodes, the left middle electrodes and the left inner electrodes are shortened from outside to inside, and the lengths of the bent sections of the right outer electrodes, the right middle electrodes and the right inner electrodes are shortened from outside to inside.

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