A micro-water content detection sensing element, sensor, preparation method and application

Abstract

The application discloses a micro-water content detection sensing element, a sensor, a preparation method and application, and the preparation method comprises the following steps: coating: taking a substrate to dip-coat an Al2O3 sol solution, so as to obtain a substrate coated with a coating; printing: printing a silver wire screen electrode on the coating surface of the substrate, so as to complete silver electrode manufacturing; heating: carrying out high-temperature oxidation treatment on the substrate after silver plating, so as to obtain a micro-water content detection sensing element. The micro-water content detection sensing element and the sensor prepared by the application have high detection precision and can be used for continuously monitoring the micro-water content in an environmentally-friendly gas insulated device.

Description

Technical Field

[0001] This invention relates to the field of detection equipment technology, specifically to a trace moisture content detection sensing element, sensor, preparation method, and application. Background Technology

[0002] Humidity measurement and control within environmentally friendly gas-insulated equipment is crucial. For safe and reliable operation, the internal moisture content needs to be maintained within specified limits. However, according to IEC 61850 and IEEE 1686, these actions are monitored by complex automated systems. Therefore, a high-precision humidity sensor capable of measuring the moisture presence in the container at the ppm level is essential. This type of sensor requires high accuracy in moisture measurement. Typically, the dew point temperature accuracy of these hygrometers should be ±0.1°C to ±0.5°C. Furthermore, this high-precision sensor complements the requirements of IEC 61850 and IEEE 1686. Various sensors utilizing different sensing principles are used to measure humidity. Even with the large number of these sensors, no single moisture measurement technology is well-suited for continuous moisture monitoring in environmentally friendly gas-insulated equipment. Dew point meters are currently an option for moisture detection; however, they are expensive and suitable for offline measurements at room temperature. Summary of the Invention

[0003] The technical problem to be solved by this invention is: how to achieve high-precision, continuous online monitoring of trace moisture content. This invention provides a trace moisture content detection sensing element, sensor, preparation method and application to solve the above problem. It has high detection accuracy and can be used to continuously monitor the trace moisture content in environmentally friendly gas insulation equipment.

[0004] This invention is achieved through the following technical solution:

[0005] A method for preparing a trace moisture content detection sensing element includes the following steps:

[0006] S1. Coating:

[0007] The substrate is dipped into an Al2O3 sol solution to obtain a substrate with a coating.

[0008] S2. Printing:

[0009] The silver electrode is fabricated by printing silver wire mesh electrodes onto the coating surface of the substrate.

[0010] S3. Heating:

[0011] The silver-plated substrate is subjected to high-temperature oxidation treatment to obtain a micro-moisture content detection sensor element.

[0012] In the above steps, for the coating, a PC-controlled automatic dip-coating machine can be used to dip-coat the prepared Al2O3 onto the cleaned substrate; by setting the descent and / or lifting speed and / or dip-coating time, Al2O3 can be coated better.

[0013] Alternatively, the substrate may be an FTO glass substrate; the substrate size may be designed to be 4cm × 1.5cm × 0.3cm.

[0014] Further, optionally, step S1 includes the following operations:

[0015] One dip-coating with Al2O3 sol solution, or at least two repeated dip-coatings with Al2O3 sol solution;

[0016] The substrate is then sintered at 400℃-550℃ for 0.5h-2h to obtain a substrate with a coating.

[0017] Amorphous γ-phase alumina (γ-Al₂O₃) is formed at temperatures above 400℃. The γ-phase contains pores of varying sizes. The pore size varies with sintering conditions. The specific surface area of ​​the sample sintered at 500℃ is approximately 230 m² / g. 2 / g. Therefore, the pore morphology confirms that the metal oxide has small pores (average pore diameter close to 8 nm) but a high surface-to-volume ratio.

[0018] Further optionally, the temperature of the Al2O3 sol solution is 680°C to 800°C (to ensure that the metal oxide Al2O3 is uniformly coated on the FTO substrate); the coating time for each coating is 20s to 25s.

[0019] Further optionally, in step S3, the oxidation treatment temperature is 300℃~400℃, and the oxidation treatment time is 2.5h~3.5h.

[0020] Through oxidation treatment, silver is able to adhere properly to the surface, become porous, and achieve its required electrical and mechanical properties.

[0021] Further, optionally, a substrate pretreatment is included before step S1;

[0022] The substrate pretreatment includes cleaning, rinsing, and drying.

[0023] More preferably, the substrate pretreatment method specifically includes:

[0024] 1) Cleaning: Remove dirt from the substrate surface using organic solvents and an ultrasonic cleaner. Multiple cleaning sessions can be performed using the same organic solvent, or multiple cleaning sessions can be performed using different organic solvents; followed by ultrasonic cleaning. Suitable organic solvents include acetone and / or ethanol. Ultrasonic cleaning time is typically 10–15 minutes.

[0025] 2) Rinse to remove residual liquid from the substrate surface;

[0026] Clean the substrate with deionized water. Rinse for 5-10 minutes.

[0027] 3) Drying to remove moisture from the substrate surface;

[0028] Dry in a dry nitrogen gas stream. The drying temperature is 50℃-70℃; the drying time is 2h-4h.

[0029] A micro-moisture content detection sensing element includes a substrate and a porous Al2O3 film layer covering the substrate, and is prepared by the above-described method for preparing a micro-moisture content detection sensing element.

[0030] A trace moisture content detection sensor includes a detection circuit and the aforementioned trace moisture content detection sensing element, wherein the detection circuit covers the surface of the detection sensing element.

[0031] Alternatively, wires are led out from the silver electrode and the substrate, and the capacitance between the silver electrode and the substrate electrode is measured as Cp. Then, the linear relationship between the trace water content in the detection environment and the capacitance of the parallel plate is:

[0032]

[0033] An application of a trace moisture content detection sensing element or sensor for detecting the moisture content in gas-insulated equipment; the sensing element is a sensing element prepared by the above-described method for preparing a trace moisture content detection sensing element, or is the above-described trace moisture content detection sensing element; the sensor is the above-described trace moisture content detection sensor.

[0034] The present invention has the following advantages and beneficial effects:

[0035] 1. The trace moisture content detection sensor element and sensor provided by this invention can realize continuous detection of moisture content in gas-insulated equipment. The response time and recovery time of the designed and manufactured sensor are as follows: Figure 6 As shown. The response time is calculated as the time it takes for the sensor output to reach 10%–90% of the total capacitance change, while the recovery time is calculated as the time it takes to reach the bottom from 90%–10% of the total change. The manufactured sensor has response and recovery times of approximately 123 and 130 seconds, respectively, indicating that the sensor can be used for continuous measurement of trace moisture content.

[0036] 2. The micro-moisture content detection sensor element, sensor and preparation method provided by the present invention are made of inexpensive materials (γ-Al2O3, FTO substrate and silver paste) and have very low manufacturing costs. The sensor design adopts a parallel plate capacitor structure, which eliminates the possibility of electrode short circuit. It is a new type of sensor that can be applied to the measurement of moisture content in environmentally friendly gas insulation equipment.

[0037] 3. The trace moisture content detection sensor element and sensor provided by this invention can effectively prevent the novel gaseous insulating medium C4F7N from corroding the internal metal materials of electrical insulation equipment at high temperatures, avoiding affecting the normal operation of electrical equipment, preventing the generation of toxic gases, and preventing safety issues for on-site maintenance personnel. This method has a simple operation process, and the materials used—silver, alumina, and FTO—are all antioxidant materials with outstanding corrosion resistance, possessing significant engineering application value.

[0038] This invention relates to a sensor element and sensor technology that uses fluorine-doped tin oxide (FTO) glass as a substrate and silver as the top electrode. A porous alumina (Al₂O₃) thin film detects the presence of moisture in the part-in-a-million (ppm) range. Experiments verified the performance of this sensor at different moisture concentrations. Within a humidity range of 246-725 ppm, this sensor technology exhibits good sensitivity (0.238 pF / ppm) and linearity (±2.05%). Simultaneously, the sensor demonstrates accurate response (±0.84%), low hysteresis (±0.32%), and high repeatability (±0.013%). Furthermore, its simple manufacturing process and robust design ensure cost-effectiveness, making it highly valuable for engineering applications. Attached Figure Description

[0039] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0040] Figure 1 This is a flowchart illustrating the preparation method of the trace moisture content detection sensor in Example 2.

[0041] Figure 2 The image shows the XRD pattern of the alumina film prepared in Example 1.

[0042] Figure 3 The image shown is a FESEM image of the alumina film prepared in Example 1.

[0043] Figure 4 This is a diagram of the test platform structure.

[0044] Figure 5 The graph shows the results of the sensitivity test.

[0045] Figure 6 The graph shows the results of the transient response test.

[0046] Figure 7 To provide an accurate test result graph.

[0047] Figure 8 The graph shows the results of the hysteresis test.

[0048] Figure 9 The graph shows the results of a highly repeatable test.

[0049] Figure 10 The graph shows the results of the stability test. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0051] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0052] Example 1

[0053] This embodiment provides a method for preparing a trace moisture content detection sensing element, the specific method of which is as follows:

[0054] Step 1, Substrate pretreatment:

[0055] Take an FTO glass substrate with dimensions of 4cm × 1.5cm × 0.3cm, and perform the following pretreatment operations in sequence:

[0056] (1) Cleaning: Use organic solvents and ultrasonic cleaners to remove dirt from the substrate surface;

[0057] First, clean the substrate in a 40°C acetone solution for 5 minutes.

[0058] Next, after removing the substrate from the acetone solution, it is placed in a 40°C ethanol solution for 5 minutes for cleaning.

[0059] Finally, place it in an ultrasonic cleaner for 10 minutes.

[0060] (2) Rinsing: Rinse off any residual liquid on the substrate surface;

[0061] Clean the substrate with deionized water to remove residual liquid from the surface.

[0062] (3) Drying: Remove moisture from the substrate surface;

[0063] The substrate was dried in a dry nitrogen gas stream. It was then dried at 60°C for 3 hours under a nitrogen atmosphere.

[0064] Step 2, Coating:

[0065] The substrate is dipped into an Al2O3 sol solution to obtain a coated substrate. The specific operation is as follows:

[0066] An automated dip-coating machine controlled by a PC was used to dip-coat the prepared Al2O3 sol solution onto a cleaned substrate. The substrate was immersed in the coating solution at a speed of 80 mm / min and lifted at a constant speed of 30 mm / min, which was repeated 10 times to achieve an Al2O3 film thickness of 10 μm on the substrate. The temperature of the Al2O3 sol solution was set at 720℃, and the immersion time for each dip was 20 s.

[0067] Then, the substrate is sintered at 500°C for 1 hour; finally, it is cooled at room temperature for 3 hours to obtain a substrate with a coating.

[0068] Step 3, Printing:

[0069] The silver electrode is fabricated by printing a silver screen electrode onto the coating surface of the substrate. Specifically, silver paste is deposited onto the sintered film of the substrate using screen printing, and the silver electrode size is 16mm × 10mm.

[0070] Step 4, heating oxidation:

[0071] The silver-plated substrate is subjected to high-temperature treatment. The entire substrate is heated at 350°C for 3 hours to allow the silver electrodes to adhere to the substrate surface and become porous, ultimately obtaining a micro-moisture content detection sensor element.

[0072] Amorphous γ-phase alumina (γ-Al₂O₃) was formed at temperatures above 400℃. The γ-phase contains pores of varying sizes. The pore size varied with sintering conditions. The pore morphology of the deposited film was investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and the Brunauer, Emmett, and Teller (BET) method. The XRD patterns of the alumina films are shown below. Figure 2 As shown. When the XRD image is compared with standard data for alumina, it shows the most significant peak of the γ phase at 2θ = 66.97, with a grain size of approximately 3 nm. FESEM images of the surface texture of the γ-Al₂O₃ film are shown below. Figure 3 As shown, this indicates the existence of nanoscale pores with an average pore size of approximately 8 nm.

[0073] Therefore, as Figure 3As shown, FESEM images reveal the nanoscale pore distribution in the thin film. BET analysis of the thin film samples was performed using a Nova 2000e instrument (Quantachrome Instruments Limited, Jamia Millia Islamia, New Delhi, USA) on different samples sintered at different temperatures, employing liquid nitrogen adsorption and desorption methods. The results indicate that the specific surface area temperature of the sample sintered at 500℃ is approximately 230 m² / s. 2 / g. Therefore, the pore morphology confirms that metal oxides have small pores but a high surface-to-volume ratio. This results in high sensitivity to low concentrations of vapor molecules, which is essential for the detection of trace moisture in SF6 gas.

[0074] Example 2

[0075] This embodiment provides a sensor fabrication method, the specific steps of which are as follows:

[0076] Step 1, Preparation of the trace moisture content detection sensor element:

[0077] The same method for preparing the micro-moisture content detection sensing element provided in Example 1.

[0078] Step 2, Assembly:

[0079] By combining a substrate with a capacitive sensing electronic circuit, a trace moisture content sensor is assembled. The cooling time at room temperature is 2 hours, after which the finished product is obtained. This sensor is then installed inside environmentally friendly gas-insulated equipment for the detection of trace moisture content within the equipment.

[0080] Wires are led out from the silver electrode and the substrate, and the capacitance between the silver electrode and the substrate electrode is measured as Cp. The linear relationship between the trace water content in the environment and the capacitance of the parallel plate is then:

[0081]

[0082] Performance testing

[0083] I. Testing Methods

[0084] 1. Sensitivity and linearity characteristics

[0085] Through such Figure 4The test platform shown was used for testing. Sensor parameters were experimentally measured using the platform illustrated above. This included a standard commercial dew point meter and the experimentally obtained sensor. The apparatus employed a computer-based data acquisition system to obtain a rapid, accurate, and reliable response from the sensor to different humidity levels in SF6 gas. A dew point generation system was used to generate airflows with different humidity levels by controlling the ratio of dry to wet gas content using a flow controller. Moisture calibration was performed using a commercial SHAW dew point meter (model: SADP, UK) with an accuracy of ±1 ppm and a full measurement range of 0-1000 ppm. The manufactured sensor was placed in a 50cc steel test chamber. The sensor was connected in series with the standard dew point meter, ensuring the moisture content within the test chamber matched the reference meter reading. The test chamber outlet was connected to a gas recovery bag to prevent SF6 gas leakage into the surrounding atmosphere. All electrical measurements of the sensor were performed using an Agilent 4294A impedance analyzer via a 16047E test fixture. The impedance analyzer output was connected to a PC via an 82357B USB / GPIB interface card.

[0086] like Figure 5 The figure shows the capacitance variation characteristics of the sensor under a fixed AC excitation [500 mV (rms) and 1 kHz]. An increase in capacitance with increasing moisture concentration was observed. This increase is attributed to the adsorption of water molecules on the film surface. The presence of the adsorbed water layer increases the apparent dielectric constant of the oxide film, thus leading to the increased capacitance.

[0087] At a frequency of 1 kHz, the sensor sensitivity is found to be 0.24 pF / ppm. Furthermore, the sensor's response is found to be highly linear, a key characteristic of the manufactured sensor. The correlation coefficient (R²) for the best-fit linear response is 0.9927, with a nonlinearity percentage of approximately 2.05% across the entire range.

[0088] 2. Transient response

[0089] like Figure 6 As shown in the figure above, the response of the fabricated sensor to a step change in the moisture concentration in SF6 gas was determined in order to test the transient response. The sensor's response time and recovery time are 123 and 130 seconds, respectively, which are within the ideal range.

[0090] 3. Accurate response

[0091] The fabricated sensor was studied using the finite element analysis software ANSYS Maxwell. The sensor design is identical to the manufactured sensor in terms of materials and dimensions (t = 10 μm, A = 10 × 16 mm). 2A 10 μm thick Al₂O₃ film was sandwiched between the electrodes. An electrostatic solution was used to analyze the designed capacitive sensor. The moisture level was altered by changing the dielectric constant of the sensing layer between the electrodes. The fabricated sensor was tested for trace moisture up to 725 ppm. At this humidity level, the number of water vapor molecules is extremely small, such as... Figure 7 As shown. Therefore, the dielectric constant of porous Al2O3 typically varies only slightly, less than 2 units.

[0092] The designed sensor exhibits a capacitance of approximately 1360.4 pF under dry conditions (εa = 9.2). The experimental capacitance under dry conditions (≈8 ppm in an N2 gas environment) is approximately 1378.06 pF. The percentage error between the experimental and simulated values ​​is only 1.29%, which is due to lead capacitance and can be compensated for using shielded short-length leads. It was observed that when the dielectric constant of the film is 10.5, the simulated capacitance is close to the capacitance obtained experimentally at a molar concentration of 725 ppm. Therefore, it can be concluded from the finite element analysis that the dielectric constant of the film changes from 9.2 to 10.5 as the moisture content in the gas environment changes from 8 ppm to 725 ppm. With increasing material dielectric constant, a polarized medium forms within the electrode. In the presence of an external electric field, the capacitance eventually increases with increasing dielectric constant. The dielectric constant increases with increasing humidity, thus increasing the polarization of the medium. The change in capacitance becomes increasingly larger with increasing polarization.

[0093] 4. Lag

[0094] The difference in adsorption and desorption rates of water molecules on the porous alumina surface leads to hysteresis error. This error was obtained by recording the sensor capacitance changes as the moisture concentration in the SF6 medium increased and decreased. Figure 8 The hysteresis curves are shown. The hysteresis error is then calculated at the point where the maximum difference between these curves is obtained. The maximum hysteresis error is found at 594 ppm, which is approximately ±0.32%.

[0095] 5. High repeatability

[0096] Repeatability curves were plotted by varying the sensor capacitance change from 246 ppm to 594 ppm at a flow rate of 6 L / min. The results are as follows: Figure 9 As shown, it can be concluded that the proposed sensor's response has a high repeatability of ±0.013%. Repeatability is calculated based on the standard deviation of the maximum capacitance value obtained over three cycles.

[0097] 6. Stability

[0098] The stability of the sensor readings at specific humidity levels and frequencies was also determined. For this experiment, the moisture content in the test chamber was maintained at primarily fixed levels of 246, 350, 550, and 594 ppm, and the sensor was excited at a fixed frequency of 1 kHz. The sensor capacitance was then continuously acquired for approximately 30 minutes using a data acquisition system. Considering the commercial application of the manufactured sensor, the sensor was tested within this humidity range. The sensor capacitance at different moisture concentrations is shown in the graph below. Figure 10 As shown in the figure, this clearly demonstrates the stability or consistency of the sensor readings. This is another important indicator of a successfully designed sensor.

[0099] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a trace moisture content detection sensing element, characterized in that, Includes the following steps: S1. Coating: The substrate is dipped into an Al2O3 sol solution to obtain a substrate with a coating. This includes a single dip-coating with an Al2O3 sol solution, or at least two repeated dip-coatings with an Al2O3 sol solution; The substrate is then sintered at 450℃~550℃ for 0.5h~2h to obtain a substrate with a coating. The temperature of the Al2O3 sol solution is 680℃ to 800℃; the immersion time for each coating is 20s to 25s. S2. Printing: The silver electrode is fabricated by printing silver wire mesh electrodes onto the coating surface of the substrate. S3. Heating: The silver-plated substrate is subjected to high-temperature oxidation treatment to obtain a micro-moisture content detection sensor element.

2. The method for preparing a trace moisture content detection sensing element according to claim 1, characterized in that, The substrate is an FTO glass substrate.

3. The method for preparing a trace moisture content detection sensing element according to claim 1, characterized in that, In step S3, the oxidation treatment temperature is 300℃~400℃ and the oxidation treatment time is 2.5h~3.5h.

4. The method for preparing a trace moisture content detection sensing element according to claim 1, characterized in that, Step S1 includes substrate pretreatment; The substrate pretreatment includes cleaning, rinsing, and drying.

5. A trace moisture content detection sensing element, characterized in that, The sensor comprises a substrate and a porous Al2O3 film covering the substrate, and is prepared using the method for preparing a micro-moisture content detection sensing element as described in any one of claims 1 to 4.

6. A trace moisture content detection sensor, characterized in that, It includes a detection circuit and a micro-moisture content detection sensing element as described in claim 5, wherein the detection circuit covers the surface of the detection sensing element.

7. A trace moisture content detection sensor according to claim 6, characterized in that, Wires are led out from the silver electrode and the substrate, and the capacitance between the silver electrode and the substrate electrode is measured. Cp The linear relationship between the trace moisture content in the detection environment and the capacitance of the parallel plate is as follows: 。 8. An application of a trace moisture content detection sensor, characterized in that, Used to detect the moisture content inside gas-insulated equipment; the sensor is a micro-moisture content detection sensor as described in claim 6 or 7.

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