A full ceramic solid-state soil ph detection device

Abstract

The application provides a full ceramic solid-state soil pH detection device, and relates to the technical field of soil environment monitoring. The full ceramic solid-state soil pH detection device comprises a protective shell, a ceramic sensing probe and a solid-state reference probe, both of which are arranged in parallel, and the front end sensing section is exposed and extends out of the protective shell; a sealed potting layer is filled in the interior of the protective shell to fix and seal the rear end of the ceramic sensing probe and the solid-state reference probe; an internal shielding wire is connected to the rear end of the ceramic sensing probe and the solid-state reference probe at one end; a signal processing and main control integrated module is arranged in the tail cavity of the protective shell and is electrically connected to the other end of the internal shielding wire; the ceramic sensing probe is made of dense phase alumina ceramic with a purity of 95%, the front end is a hemispherical sensing end, and the rear end is provided with a high-temperature sintering and infiltrating conductive layer. The full solid-state integrated structure is stable and suitable for field in-situ monitoring.

Description

Technical Field

[0001] This invention relates to the field of soil environmental monitoring technology, specifically to an all-ceramic solid soil pH detection device. Background Technology

[0002] Soil pH measuring devices are specialized electrochemical sensors used to measure soil acidity and alkalinity, and are widely used in fields such as farmland soil health assessment, crop growth environment monitoring, saline-alkali land improvement, and ecological restoration. These devices typically consist of a pH-sensitive element, a reference element, and a signal acquisition unit. They detect the hydrogen ion activity in soil pore water and calculate the corresponding pH value using the Nernst equation. Currently, common soil pH measuring devices mainly include glass electrode types, metal electrode types, and a few solid-state ion-selective electrode types.

[0003] While existing soil pH testing devices using glass electrodes offer high accuracy in laboratory liquid environments, their core components consist of an extremely thin, specialized glass sensing membrane and an internally filled liquid reference electrolyte. When used for long-term in-situ soil monitoring, the liquid electrolyte is prone to drying out and leakage under alternating soil moisture and temperature conditions, leading to a drift in the reference potential. This necessitates frequent disassembly, replenishment, and recalibration, failing to meet the demands of large-scale, unattended, continuous monitoring in the field. Consequently, this directly restricts the long-term reliability of in-situ soil pH data and the efficiency of equipment deployment. Summary of the Invention

[0004] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an all-ceramic solid soil pH testing device, which solves the problem that existing liquid electrolytes are prone to drying out and leakage, requiring frequent maintenance and testing.

[0005] Technical solution To achieve the above objectives, the present invention provides the following technical solution: a fully ceramic solid soil pH detection device, comprising: Protective casing; A ceramic sensing probe and a solid-state reference probe are arranged in parallel, with the front sensing section exposed and extending out of the protective shell; A sealing potting layer is filled inside the protective housing to fix and seal the rear ends of the ceramic sensing probe and the solid reference probe. An internally shielded wire is connected at one end to the rear end of the ceramic sensing probe and the solid-state reference probe, respectively. The signal processing and main control integrated module is located in the rear cavity of the protective housing and is electrically connected to the other end of the internal shielded wire; The ceramic sensing probe is made of high purity 95% dense It is made of alumina ceramic, with a hemispherical induction end at the front end and a high-temperature sintered conductive layer at the rear end; The solid reference probe includes a porous ceramic sleeve, a polymer solid electrolyte filled inside the sleeve, and a metal reference core wrapped inside the polymer solid electrolyte. The probe has a rear sealing section at the rear end.

[0006] Preferably, the substrate of the ceramic sensing probe is a high-purity alumina ceramic matrix with a purity of 99%, and the hemispherical sensing tip is integrally formed with the high-purity alumina ceramic matrix.

[0007] Preferably, in the solid reference probe, the porous ceramic sleeve has an alumina purity of 85%-90% and its grain boundaries contain an amorphous glass phase; the polymer solid electrolyte is a composite solid electrolyte doped with lithium bis(trifluoromethanesulfonyl)imide in a polyvinylidene fluoride-hexafluoropropylene blend matrix; the metal reference core is an Ag / AgCl core; and the rear sealing section is an epoxy resin sealing layer.

[0008] Preferably, the sealing potting layer is an epoxy resin fully sealing potting layer.

[0009] Preferably, the signal processing and main control integrated module includes an input impedance. operational amplifiers and 24-bit Modular-to-digital converter unit.

[0010] Preferably, the ceramic sensing probe and the solid-state reference probe are arranged coaxially and parallel, and the exposed lengths of their front sensing sections are equal.

[0011] A soil pH monitoring system, characterized in that it comprises: At least one all-ceramic solid soil pH testing device according to any one of claims 1 to 6, and a remote monitoring platform; The signal processing and main control integration module of the all-ceramic solid soil pH detection device is equipped with an RS485 communication interface, which is connected to the remote monitoring platform via a bus or wireless transmission module.

[0012] Preferably, the wireless transmission module is a LoRa spread spectrum communication module or a 4G wireless transmission module.

[0013] Preferably, the signal processing and main control integration module has a quadratic binomial regression fitting coefficient embedded in it, which is used to convert the differential potential difference into a pH value output.

[0014] Beneficial effects This invention provides an all-ceramic solid soil pH detection device. It has the following beneficial effects: 1. This invention provides an all-ceramic solid soil pH detection device. The invention adopts an all-solid integrated dual-probe structure. Neither the ceramic sensing probe nor the solid reference probe contains liquid electrolyte or fragile sensitive membrane. Combined with epoxy resin full-sealing potting treatment, the risk of electrolyte leakage and drying is completely eliminated, which significantly optimizes the long-term service stability of the device in complex soil environments and eliminates the need for periodic maintenance.

[0015] 2. This invention provides an all-ceramic solid soil pH detection device. Utilizing the proton reversible response characteristics of the natural hydroxyl groups on the surface of high-purity alumina ceramics, combined with high-impedance signal acquisition and a three-point calibration quadratic fitting algorithm, this invention effectively suppresses the interference of soil salinity, humidity, and temperature fluctuations on the detection signal, promoting error control within a certain range. Within 0.05 pH, it significantly improves in-situ detection accuracy and temporal consistency compared to existing glass and metal electrodes. Attached Figure Description

[0016] Figure 1 This is an isometric view of the present invention; Figure 2 This is a cross-sectional schematic diagram of the present invention; Figure 3 This is a schematic diagram of the axial side of the ceramic sensing probe of the present invention; Figure 4 This is a cross-sectional schematic diagram of the solid-state reference probe of the present invention; Figure 5 This is a schematic diagram of the system flow of the present invention.

[0017] The components include: 1. Protective shell; 2. Ceramic sensing probe; 3. Solid-state reference probe; 4. Sealing potting layer; 5. Internal shielding wire; 6. Signal processing and main control integrated module; 201. High-purity alumina ceramic substrate; 202. Hemispherical sensing tip; 203. Rear end sintered conductive layer; 301. Porous ceramic sleeve; 302. Polymer solid electrolyte; 303. Metal reference core; 304. Rear end sealing section. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 like Figure 1As shown, this embodiment provides an all-ceramic solid soil pH detection device, including a protective shell 1, a ceramic sensing probe 2, a solid reference probe 3, a sealing potting layer 4, an internal shielding wire 5, and a signal processing and main control integrated module 6. The protective shell 1 is a cylindrical metal or engineering plastic shell with an axial length of 120mm-150mm and an outer diameter of 18mm-22mm. The ceramic sensing probe 2 and the solid reference probe 3 are arranged parallel and coaxially inside the protective shell 1, with their front sensing sections exposed and extending beyond the front face of the protective shell 1 by a length of 25mm-35mm, for direct insertion into the soil to be tested.

[0020] A sealing and potting layer 4 fills the interior of the protective housing 1, completely encapsulating and fixing the rear end of the ceramic sensing probe 2, the rear end of the solid-state reference probe 3, and the connection point of the internal shielded wire 5. Specifically, in the above embodiment, the sealing and potting layer 4 uses a two-component epoxy resin, which is potted and molded under vacuum conditions, and after curing, forms a dense, bubble-free seal. This sealing structure has no external liquid-cooled components, no venting or pressure relief channels, and no exposed electrode wiring ports, achieving an overall waterproof rating of IP68. Compared to the segmented splicing sealing method used in traditional pin-type pH sensors, the fully sealed structure of this invention significantly optimizes the moisture-proof performance under long-term buried conditions, eliminating the signal drift problem caused by water vapor seeping into the housing along the probe gaps.

[0021] The internal shielded conductor 5 is a dual-core shielded cable. One end is soldered to the high-temperature sintered conductive layer 203 at the rear end of the ceramic sensing probe 2 and the metal reference core 303 at the rear end of the solid-state reference probe 3, respectively. The other end is connected to the input terminal of the signal processing and main control integration module 6. The signal processing and main control integration module 6 is located in the rear cavity of the protective housing 1. This cavity is separated from the front probe mounting area by a sealing potting layer 4 to ensure that the electronic components do not come into contact with any moisture.

[0022] It should be noted that the signal processing and main control integrated module 6 of this invention is not simply a conventional pH acquisition circuit placed inside the housing, but rather is specifically designed to address the ultra-high internal resistance characteristics of the alumina ceramic probe (measured DC internal resistance). The input impedance was specially designed. A junction field-effect operational amplifier is used as a pre-buffer stage. If a common op-amp (with an input impedance typically of...) is used... If this occurs, the probe interface potential will be significantly lowered, causing the pH measurement value to deviate from the true value by 0.3 to 0.5 units. The specific circuit configuration of this module will be detailed in Example 3.

[0023] Example 2 like Figure 2As shown, the ceramic sensing probe 2 includes a high-purity alumina ceramic substrate 201, a hemispherical sensing tip 202 integrally formed at the front end, and a high-temperature sintered conductive layer 203 disposed at the rear end. The high-purity alumina ceramic substrate 201 is selected with a purity of 99%. Alumina powder, after isostatic pressing, is sintered at 1650℃-1700℃ for 68 hours to obtain a dense powder. 98% of the ceramic rods are 6mm in diameter and 50mm in length. The hemispherical sensing tip 202 is formed by mechanical grinding and polishing, with a surface roughness of... The high-temperature sintering conductive layer 203 uses silver or platinum paste, sintered at 800℃-900℃ for 20 minutes to form a thickness of [thickness missing]. The dense metal layer, pull-out force after soldering leads 5N.

[0024] Specifically, in the above embodiments, the alumina ceramic purity was chosen to be 99% instead of 95% to ensure optimal areal density of the surface hydroxyl active sites. Tests show that 99% purity... In simulated soil pore water (pH 4–10), the surface hydroxyl density of alumina ceramics is approximately 4.5 hydroxyl groups / cell. Materials with a purity of 95% contain a small amount of glass phase (mainly...) (CaO), hydroxyl density decreased to 3.2 / This results in a decrease in response sensitivity of approximately 15%. Therefore, for applications requiring full-range error... For high-precision applications requiring 0.05 pH, 99% high-purity alumina ceramics are preferred; for general agricultural monitoring, 95% ceramics are also sufficient. The required accuracy is 0.1 pH.

[0025] like Figure 3 As shown, the solid-state reference probe 3 includes a porous ceramic sleeve 301, a polymer solid electrolyte 302, a metal reference core 303, and a rear sealing section 304. The porous ceramic sleeve 301 has an outer diameter of 8 mm, an inner diameter of 4 mm, and a length of 40 mm. It is made from industrial-grade alumina powder with a purity of 88%, with 5% kaolin and 3% talc as sintering aids, and is sintered at 1250℃-1300℃ for 2 hours. Its porosity is 40%-50%, and a continuous amorphous glass phase is formed at the grain boundaries. This glass phase covers the active hydroxyl sites on the surface of the alumina grains, so that the porous ceramic sleeve 301 itself does not have hydrogen ion response capability, but only serves as a physical carrier for the solid electrolyte.

[0026] It is important to note that the solid-state reference probe of this invention is intentionally made of alumina, a material with a purity diametrically opposed to that of the sensing probe, with a purity difference exceeding 10 percentage points and a significant difference in the content of the grain boundary glass phase. If the same high-purity ceramic as the sensing probe were used as the reference probe sleeve, the reference probe would also exhibit a weak pH response. Although this could be partially offset by a differential circuit, the medium- to long-term baseline drift caused by the difference in temperature drift coefficients could still reach 0.2 pH / month. The differentiated design of this invention eliminates cross-interference at the material level, promoting the long-term stability of the reference potential.

[0027] A polymeric solid electrolyte 302 fills the internal cavity and pores of a porous ceramic sleeve 301. Its specific composition is as follows: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) as the matrix, with a mass fraction of 70%; lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the ion-conducting aid, with a mass fraction of 30%; and a small amount of propylene carbonate as a plasticizer. In preparation, the above components are dissolved in acetone, cast into the inner cavity of the porous ceramic sleeve, and vacuum dried at 60°C for 48 hours to obtain a solid electrolyte membrane free of liquid solvents and volatile components. AC impedance testing shows that the ionic conductivity of this electrolyte at 25°C is [value missing]. The conductivity changes by no more than one order of magnitude within the temperature range of -20℃ to 60℃.

[0028] The metal reference core 303 is an Ag / AgCl wire with a diameter of 0.8 mm and a length of 15 mm, completely encapsulated within the polymer solid electrolyte 302, at least 5 mm from the front end of the sleeve. Its rear end is led out via a silver-plated copper lead wire and encapsulated by the rear sealing section 304. The rear sealing section 304 is made of high-temperature resistant epoxy resin, cured at 80°C for 2 hours to form a dense sealing layer 5 mm thick, preventing moisture from seeping in along the lead wire gaps.

[0029] Example 3 The signal processing and main control integrated module 6 includes a differential impedance conversion buffer circuit, an analog-to-digital conversion unit, a main control and arithmetic unit, and an RS485 communication circuit, which are connected in sequence. All units are integrated on a 16mm diameter double-sided PCB and are encapsulated in the rear of the protective housing 1.

[0030] The core components of the differential impedance conversion buffer circuit are two Analog Devices (ADI) ADA4530-1 op-amps. These op-amps typically have an input bias current of 20 fA and an input impedance of... The common-mode rejection ratio is 130dB (typical). The circuit adopts a differential symmetrical architecture: the signal from ceramic sensing probe 2 is connected to the non-inverting input, the signal from solid-state reference probe 3 is connected to the inverting input, and the output provides a low-impedance voltage signal linearly related to the potential difference between the two probes. The voltage noise density of this buffer circuit is... The electrochemical noise is much lower than that of the alumina probe itself (approximately). This ensures that the signal is transmitted without distortion.

[0031] Specifically, in the above specific embodiments, the reason why a junction field-effect transistor input stage op-amp must be used instead of a general CMOS op-amp is that the interface contact resistance of the alumina probe can reach 1G when it is in dry soil or in contact with soil with low moisture content. The above is true. If a general-purpose op-amp with an input bias current of 1pA is used, the bias voltage drop across this resistor will be 1mV, which is equivalent to an error of 0.06pH; while if an ADA4530 with an input bias current of 20fA is used, the error generated under the same conditions will be only 0.0012pH, which is negligible.

[0032] The analog-to-digital converter unit selected is the ADS1262 24-bit. This is a type of ADC with a built-in programmable gain amplifier (PGA), whose gain can be set from 1 to 128 times. In this embodiment, the PGA gain is set to 16 times, which will output the probe... 500mV differential signal amplified to The ADC operates within an 8V range, matching its full-scale input. The ADC sampling frequency is set to 20Hz, achieving an effective resolution (ENOB) of 21.5 bits. After arithmetic averaging filtering using 100 consecutive samples, the potential difference resolution is better than 0.01mV, corresponding to a pH resolution better than 0.001.

[0033] The main control unit uses an STM32L051 low-power Cortex-M0+ microcontroller with an operating frequency of 32MHz. Its built-in flash memory contains calibration fitting coefficients, temperature compensation algorithms, and data protocol processing programs. The RS485 communication circuit uses an ADM2483 isolated transceiver to achieve electrical isolation between analog and digital grounds, with an isolation withstand voltage of up to 2.5kV, effectively blocking interference from soil ground potential fluctuations on digital signals.

[0034] It is important to note that the fundamental difference between the signal processing module of this invention and conventional pH transmitters lies in the following: Conventional devices transmit the probe analog signal to an external transmitter via a long cable (typically 1-5 meters). The cable's distributed capacitance (approximately 100 pF / m) and the probe's high internal resistance form a low-pass filter, resulting in a response time exceeding 30 seconds and susceptibility to power frequency interference. In contrast, this invention places the buffer circuit close to the probe's rear end, with a lead length from the probe to the buffer circuit of less than 20 mm and a distributed capacitance of less than 2 pF. This shortens the response time to less than 1 second, and the fully differential structure combined with a common-mode choke improves the power frequency interference suppression ratio to over 80 dB.

[0035] Example 4: Specific Implementation of the Three-Point Calibration and Quadratic Fitting Algorithm This embodiment describes how to establish a potential-pH mapping relationship during factory calibration or field calibration. According to JJF1196-2008 "Outline for Type Evaluation of pH Meters", three sets of standard buffer solutions were selected: pH 4.01 (potassium hydrogen phthalate, 25°C), pH 6.86 (mixed phosphate, 25°C), and pH 9.18 (borax, 25°C). All buffer solutions should be freshly prepared or use certified reference materials, and the temperature error should be controlled within [specific parameters]. Within 0.2℃.

[0036] The calibration process is as follows: First, completely immerse the hemispherical sensing tip of the probe in a pH 4.01 buffer solution, ensuring the liquid level is at least 20 mm above the sensing tip. Let it stand for 60 seconds to allow the interfacial proton reaction to reach thermodynamic equilibrium (manifested as a potential shift). (0.1mV / min). Differential potential values ​​were continuously collected over 30 seconds, and the arithmetic mean was taken, denoted as... In this embodiment, the actual measurement... (Reference probe).

[0037] The second step is to remove the probe, rinse it thoroughly with deionized water, and blot it dry with filter paper. Then, immerse it sequentially in pH 6.86 and pH 9.18 buffer solutions, repeating the above steps to obtain the measured values. , .

[0038] The third step is to input the three sets of calibration data into the least squares quadratic regression algorithm built into the main control unit. Let the potential difference be... Let x be the independent variable and pH be the dependent variable y. The fitting equation is: Where a, b, and c are the coefficients to be determined. The three sets of data... , , Substituting the values, we obtain a system of three linear equations in three variables: Solving this system of equations, we get: Specifically, in the above specific embodiments, the advantage of the quadratic fitting model compared to the traditional two-point linear fitting method (using only pH 4.01 and pH 6.86) can be quantified as follows: the maximum residual of the linear fitting method in the pH range of 4~9 is... The residual value of the quadratic fitting method was 0.12 pH, occurring near pH 8.5; while the root mean square residual value was 0.018 pH, with a maximum residual of 0.034 pH. The table below compares the two methods at various standard points: Therefore, it can be seen that quadratic fitting reduces the full-range error from pH dropped from 0.13 Below 0.02 pH, detection accuracy is significantly optimized.

[0039] After calibration, coefficients a, b, and c are permanently stored in the flash memory of the main control unit and are not lost when power is off. Because the alumina ceramic probe exhibits extremely low aging drift (less than 1 mV / month after continuous immersion in a pH 7 soil simulation solution for 60 days), under normal field monitoring conditions, recalibration every 3 months is sufficient to maintain its performance. The accuracy index is 0.05 pH.

[0040] Example 5: Implementation of Temperature Compensation This embodiment adds a temperature compensation function to embodiment 4. For example... Figure 1 As shown, a PT1000 platinum resistance temperature sensor (not shown separately in the attached diagram, but mounted close to the inner wall of the protective housing) is mounted on the PCB of the signal processing and main control integration module 6. The main control unit reads the temperature value every 10 seconds, with a resolution of 0.01℃.

[0041] Temperature compensation is based on a modified Nernst equation. For an ideal hydrogen ion-selective electrode, the electrode potential E is related to pH as follows: in , T is the thermodynamic temperature (K). At 25℃ (298.15K), the Nernst slope is 59.16mV / pH; as the temperature deviates from 25℃, the slope changes proportionally.

[0042] The measured Nernst slope of the alumina ceramic probe of this invention is 98%-102% of the theoretical value in the range of 15-45℃. To achieve accurate compensation, during the calibration process, the temperatures T1, T2, and T3 corresponding to three calibration points are recorded simultaneously (typically, these three are equal under constant temperature conditions), and temperature is introduced as an independent variable into the fitting model. The extended calibration equation is: in The reference temperature is 25°C, and d is the temperature coefficient, obtained by linear regression of the measurement deviation of the device for the same buffer solution at different temperatures (e.g., 15°C, 25°C, 45°C). In this embodiment, the actual measurement... .

[0043] It is important to note that existing glass electrode temperature compensation techniques typically only correct the Nernst slope, neglecting the temperature drift of the liquid junction potential and asymmetric potential. The solid-state probe of this invention has no liquid junction structure, and its temperature drift originates from only two sources: firstly, the minute change in the proton association / dissociation equilibrium constant of the hydroxyl groups on the ceramic surface (approximately -0.0015 pH / ℃); and secondly, the temperature dependence of the ionic conductivity of the reference probe solid electrolyte (approximately -0.0013 pH / ℃). The combined value is -0.0028 pH / ℃, which is more than half the typical temperature drift coefficient of glass electrodes (-0.005 to -0.01 pH / ℃).

[0044] Example 6: System-level networking application This embodiment provides a soil pH monitoring system, including multiple all-ceramic solid soil pH detection devices as described in Embodiments 1 to 5, and a remote monitoring platform. Each device is connected in parallel to the same twisted-pair bus via its RS485 communication interface, with a bus length of up to 1200 meters. Each device has a unique Modbus RTU address (1~247). The main control unit sequentially reads the pH data from each device in a polling manner. The data frame format is: address code (1 byte), function code (03), register start address (2 bytes), number of registers (2 bytes), and CRC checksum (2 bytes). Each device stores the latest collected pH value (retaining two decimal places) in a holding register.

[0045] For wireless deployment scenarios, an RS485 bus connects to a LoRa gateway. The gateway converts the data into LoRaWAN protocol packets and transmits them to a remote monitoring platform via the 470MHz / 510MHz frequency band. In open farmland environments, the LoRa communication distance can reach 35 kilometers. Alternatively, a 4G DTU can be used to convert the RS485 signal to TCP / IP protocol and transmit it to a cloud server via an operator's base station. The monitoring platform is equipped with a database and a web front-end, which can display the pH value, temperature, battery voltage (if solar-powered), and historical trend curves of each monitoring point in real time. It also automatically sends SMS or WeChat alarms when the pH exceeds a set threshold (e.g., <5.5 or >8.5).

[0046] Specifically, in the above embodiments, since the device of the present invention directly outputs RS485 digital signals without the need for any external transmitters or data acquisition cards, the cost per node is reduced by approximately 40% compared to the traditional analog electrode + external transmitter solution, and the common-mode interference problem of long-distance analog signal transmission is avoided. Actual testing showed that with 15 of these devices connected to a 300-meter RS485 bus, the pH reading at the end node differed from that at the near-end node by no more than 0.02 pH, verifying the high reliability of the digital transmission.

[0047] Example 7: Equivalent Material Replacement Example This embodiment illustrates the selection of equivalent materials for the ceramic sensing probe 2. Besides 99% high-purity alumina ceramic, the following materials, provided they possess surface hydroxyl proton response characteristics, can also achieve the core function of this invention: Material A: High-purity zirconia ceramic (ZrO2, purity) (99%), stabilized with 3 mol% yttrium oxide. Its surface hydroxyl density is approximately 3.8 hydroxyl groups / The response sensitivity was 56.2 mV / pH (25℃), slightly lower than that of alumina, but the mechanical fracture toughness was higher. Alumina is It is suitable for extreme soil environments with a high content of sand and gravel.

[0048] Material B: Zinc oxide-based composite ceramic (ZnO doped) It is sintered using standard ceramic processes. Its surface hydroxyl density reaches 5.1 hydroxyl groups / year. The sensitivity is 60.1 mV / pH, close to the theoretical value. However, zinc oxide undergoes slight dissolution in acidic soils with pH < 5, with an annual dissolution rate of approximately [missing value]. Its long-term service life is slightly shorter than that of alumina. This material is suitable for monitoring scenarios in neutral to alkaline soils (pH 6~9).

[0049] Material C: Magnesium oxide-doped modified ceramic (MgO doping amount 5wt%, matrix is...) This material combines the chemical stability of alumina with the high hydroxyl density (4.9 hydroxyl groups / ) of magnesium oxide. It has a sensitivity of 58.7 mV / pH and better resistance to alkali corrosion than alumina, making it particularly suitable for long-term monitoring in saline-alkali land (pH 8~10).

[0050] It should be noted that the scope of protection for the aforementioned equivalent materials is not unlimited. All oxide ceramics employing the three core technological principles of lattice defect-derived hydroxyl interfaces, all-solid-state film-free probes, and proton reversible response detection, regardless of purity fine-tuning, trace metal ion doping, or sintering process modification, fall within the scope of equivalent protection of this invention. However, the following materials are excluded: ① inert ceramics that require surface modification with noble metals (Pt, Au) to produce a pH response; ② composite electrodes that require coating with polymer-sensitive films (such as polyaniline, polypyrrole); ③ materials based on the principle of metal-metal oxide galvanic cells (such as...). The electrodes of this invention have a different response mechanism than those of the present invention.

[0051] Example 8: Long-term buried stability test data This embodiment provides long-term stability test data of the device of the present invention in a real soil environment to demonstrate its maintenance-free characteristics.

[0052] Test site: A farmland in the North China Plain, with alluvial soil, a background pH of 7.8-8.2, a salt content of 0.15%, and an organic matter content of 1.8%. The device of this invention (a total of 10 units, numbered S1-S10) was vertically buried in the soil, with the probe tip completely buried in the topsoil (10cm-20cm deep), and the protective casing protruding approximately 5cm above the surface for data reading. Control devices were also buried simultaneously: 3 glass electrode pH probes (maintenance-free type, but still containing liquid electrolyte) and 3 metal electrode probes. All devices were connected to a data logger, recording pH values ​​hourly.

[0053] Testing period: 180 days (6 months). No calibration, cleaning, or maintenance operations will be performed during this period. Soil samples will be manually collected from near the burial site on days 0, 30, 60, 90, 120, 150, and 180, and the laboratory reference pH value will be determined according to the national standard method (NY / T1377-2007) as a true reference.

[0054] The test results are summarized in the table below: Note: Drift = Measured value - Laboratory reference value; a negative value indicates that the measured value is too low.

[0055] During the testing period, the standard deviation of the readings of all 10 devices of this invention was less than 0.04 pH at any time point, with the maximum individual drift being +0.05 pH (S7 at 180 days). In contrast, the glass electrode drifted by an average of +0.82 pH after 180 days due to the drying of the internal electrolyte and the drift of the liquid junction potential; the metal electrode drifted by an average of -1.15 pH due to surface oxidation and passivation. Furthermore, two glass electrodes completely failed (readings exceeded the range) around day 120, and one metal electrode corroded and broke at day 150.

[0056] The above test data shows that the all-ceramic solid soil pH detection device of the present invention can still maintain its performance under continuous buried maintenance-free conditions for up to 6 months. With a detection accuracy within 0.05 pH, it is significantly better than existing glass and metal electrodes, fully meeting the reliability requirements of long-term in-situ data for smart agriculture and ecological monitoring in open fields.

[0057] Example 9 This embodiment provides a method for preparing an apparatus suitable for mass production.

[0058] Step 1: Preparation of ceramic sensing probes. Commercially available 99% high-purity ceramic probes were selected. Powder (average particle size 0.5) ), with 0.5 wt% polyvinyl alcohol added as a binder, after ball milling and mixing for 4 hours, it was isostatically pressed into shape under a pressure of 120 MPa. The blanks were placed in a sintering furnace and heated to 600℃ at a rate of 2℃ / min to remove the binder, holding for 2 hours; then heated to 1680℃ at a rate of 5℃ / min and held for 4 hours; finally cooled to room temperature in the furnace. The linear shrinkage of the sintered ceramic rods was approximately 18%, and the final dimensions were [missing information]. One end is machined into a hemispherical shape on a surface grinder and polished to a mirror finish using 200#, 600#, and 1200# diamond grinding discs in sequence. A 5mm long area at the rear end is coated with silver paste and fired at 850℃ for 20 minutes to form a conductive layer.

[0059] Step 2: Preparation of solid-state reference probe. Weigh alumina powder (88% purity, d50=2). Add 5% kaolin, 3% talc, and 0.3% methylcellulose, mix thoroughly by dry method, and then mold into a sleeve blank with an outer diameter of 9mm, an inner diameter of 5mm, and a length of 45mm under a pressure of 80MPa. Place it in a sintering furnace, heat to 1280℃ at a rate of 3℃ / min, hold for 2 hours, and then cool with the furnace. The resulting porous ceramic sleeve shrinks to an outer diameter of 8mm, an inner diameter of 4.5mm, a length of 40mm, and a porosity of approximately 45%. Insert an Ag / AgCl wire (0.8mm in diameter) into the bottom of the sleeve, with the wire end 5mm from the front end of the sleeve. Prepare a mixed solution of PVDF-HFP (Solef21216) and LiTFSI (3M) in a mass ratio of 7:3, using acetone as the solvent, with a solid content of 15%. Inject the solution into the inner cavity of the sleeve and place it in a vacuum drying oven at 60℃ for 72 hours until the solvent has completely evaporated, obtaining a solid electrolyte. The lead wire is led out from the rear end, and the rear 10mm length area is potted with epoxy resin and cured at 80℃ for 2 hours.

[0060] Step 3: Housing Assembly and Encapsulation. Insert the two probes parallel into the protective housing 1 (injection-molded PPS plastic housing with internal positioning grooves), ensuring the front sensing section extends 30mm. Solder the probe rear leads to the internal shielded wires 5. Insert the PCB board of the signal processing and main control integration module 6 into the slot at the rear of the housing and connect the wires. Inject epoxy resin (3MDP270) through the injection hole on the side of the housing using a syringe until the resin overflows from the vent hole. Cure in a 60℃ oven for 4 hours. After curing, the rear of the housing can be further fitted with an M12 waterproof connector (RS485 lead wire) or pre-installed with a 3-meter cable.

[0061] Step 4: Calibration and Testing. Perform three-point calibration as described in Example 4, calculate the fitting coefficient, and write it into the main control unit. Then, test the standard buffer solutions at pH 4.01, pH 6.86, and pH 9.18 sequentially. The error should be within [a certain range]. Within 0.03 pH; for testing phosphate buffer at pH 7.00, continuous sampling for 1 hour should result in a potential drift of less than 0.5 mV. Qualified products are labeled with a unique serial number and packaged for shipment.

[0062] Working Principle: This invention utilizes hydroxyl active sites formed by the adsorption of water molecules on oxygen vacancies and lattice defects on the surface of high-purity alumina ceramics. In the soil pore electrolyte environment, hydroxyl groups undergo reversible proton association or dissociation reactions with hydrogen ions, forming a double-layer polarization potential at the solid-liquid interface that exhibits a Nernst relationship with hydrogen ion activity. A ceramic sensing probe acquires this interfacial potential, while a solid-state reference probe provides a stable reference potential. The differential signal between the two is buffered by a high input impedance circuit and converted from analog to digital. Then, it is calibrated by a built-in quadratic binomial regression model and a temperature compensation coefficient, ultimately resolving to the soil pH value. This process eliminates the need for liquid electrolytes and polymer-sensitive membranes, resulting in low electrochemical baseline drift and promoting repeatability and consistency under long-term buried conditions.

[0063] The above description is merely a preferred 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.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fully ceramic solid soil pH detection device, characterized in that, include: Protective outer casing (1); The ceramic sensing probe (2) and the solid reference probe (3) are arranged in parallel, with the front sensing section exposed and extending out of the protective shell (1). A sealing potting layer (4) is filled inside the protective shell (1) to fix and seal the rear ends of the ceramic sensing probe (2) and the solid reference probe (3); An internal shielded wire (5) is connected at one end to the rear end of a ceramic sensing probe (2) and a solid reference probe (3), respectively. The signal processing and main control integrated module (6) is located in the rear cavity of the protective shell (1) and is electrically connected to the other end of the internal shielded wire (5); The ceramic sensing probe (2) is made of high purity 95% dense It is made of alumina ceramic, with a hemispherical induction end (202) at the front end and a high-temperature sintered conductive layer (203) at the rear end. The solid reference probe (3) includes a porous ceramic sleeve (301), a polymer solid electrolyte (302) filled inside the sleeve, and a metal reference core (303) wrapped inside the polymer solid electrolyte (302). The probe has a rear sealing section (304) at the rear end.

2. The all-ceramic solid soil pH detection device according to claim 1, characterized in that, The substrate of the ceramic sensing probe (2) is a high-purity alumina ceramic matrix (201) with a purity of 99%, and the hemispherical sensing end (202) is integrally formed with the high-purity alumina ceramic matrix (201).

3. The all-ceramic solid soil pH detection device according to claim 1, characterized in that, In the solid reference probe (3), the porous ceramic sleeve (301) has an alumina purity of 85%-90% and its grain boundaries contain an amorphous glass phase; the polymer solid electrolyte (302) is a composite solid electrolyte doped with lithium bis(trifluoromethanesulfonyl)imide in a polyvinylidene fluoride-hexafluoropropylene blend matrix; the metal reference core (303) is an Ag / AgCl core; and the rear sealing section (304) is an epoxy resin sealing layer.

4. The all-ceramic solid soil pH detection device according to claim 1, characterized in that, The sealing and potting layer (4) is an epoxy resin fully sealed potting layer.

5. The all-ceramic solid soil pH detection device according to claim 1, characterized in that, The signal processing and main control integrated module (6) includes input impedance operational amplifiers and 24-bit Modular-to-digital converter unit.

6. The all-ceramic solid soil pH detection device according to claim 1, characterized in that, The ceramic sensing probe (2) and the solid reference probe (3) are arranged coaxially and parallel, and the exposed lengths of their front sensing sections are equal.

7. A soil pH monitoring system, characterized in that, include: At least one all-ceramic solid soil pH testing device according to any one of claims 1 to 6, and a remote monitoring platform; The signal processing and main control integration module (6) of the all-ceramic solid soil pH detection device is equipped with an RS485 communication interface, which is connected to the remote monitoring platform through a bus or wireless transmission module.

8. The soil pH monitoring system according to claim 7, characterized in that, The wireless transmission module is a LoRa spread spectrum communication module or a 4G wireless transmission module.

9. The soil pH monitoring system according to claim 7, characterized in that, The signal processing and main control integration module (6) contains quadratic binomial regression fitting coefficients, which are used to convert differential potential difference into pH value output.

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