A liquid level detection method, an interdigital electrode structure, a liquid level sensor and a medium

Abstract

This invention discloses a liquid level detection method, an interdigitated electrode structure, a liquid level sensor, and a medium. The method is applicable to liquid level sensors equipped with dual-frequency excitation circuits and includes: acquiring the actual measured capacitance value and liquid level height, as well as a reference capacitance value when the container is unloaded; constructing a mapping model between the liquid level height and the differential value; acquiring a reference capacitance value; if the change in the reference capacitance value exceeds a threshold range, determining to update the mapping model; and calculating the real-time liquid level value using the updated mapping model. This application uses differential calculation of capacitance values ​​from dual-frequency signals to suppress interference from the dielectric constant of the medium, balancing measurement accuracy, anti-interference, and response speed. Furthermore, by using the reference capacitance value acquired by the reference electrode to set up a mapping model update mechanism, it actively responds to the impact of environmental changes on the mapping model, expanding the dynamic range of liquid level detection to improve the anti-interference, accuracy, and robustness of real-time detection, making it applicable to various scenarios in real-world situations.

Description

Technical Field

[0001] This invention relates to the field of liquid level detection technology, specifically to a liquid level detection method, an interdigitated electrode structure, a liquid level sensor, and a medium. Background Technology

[0002] Liquid level detection is of great value in medical, biological experiments, and industrial automation. Existing technologies, such as float-type, ultrasonic, and optical liquid level sensors, suffer from drawbacks such as large size, susceptibility to media interference, or the need to penetrate containers.

[0003] Capacitive level sensors have attracted attention due to their simple structure, fast response, and miniaturization. Their basic principle is based on the change in dielectric constant between electrodes caused by changes in liquid level, resulting in a change in capacitance. By detecting this capacitance, the liquid level can be deduced.

[0004] To improve the accuracy and adaptability of capacitive liquid level sensors, Chinese patent application CN108871498A discloses a capacitive adaptive universal liquid level measurement device and method. This method utilizes capacitance-frequency conversion combined with a reference electrode to improve measurement consistency and introduces an environmental sensor to detect system faults. Chinese patent CN115900884B discloses an adaptive capacitive liquid level sensor that decouples liquid level calculation from the dielectric constant of the medium by setting a reference electrode and a specific algorithm. However, both of these solutions rely on rigid substrates for electrode fabrication, which cannot be bent or deformed. Once a container of different size or curvature (such as a test tube or medicine bottle) is replaced, a new sensor must be customized, resulting in fundamental drawbacks such as high deployment costs and poor versatility.

[0005] To address the technical shortcomings of rigid substrates in terms of poor adaptability, Chinese patent CN213274466U discloses a capacitive external sensing liquid level detector. This detector utilizes a flexible PET film and printed conductive and insulating ink layers to form a flexible sensing device, achieving non-contact detection through capacitive sensing circuitry. However, this solution employs only a single-layer electrode structure, resulting in uneven electric field distribution at the edges. This leads to a sharp drop in sensitivity at low or high liquid levels, limiting the dynamic range and making it difficult to meet the requirements for high-precision monitoring across the entire liquid range.

[0006] Furthermore, to improve the anti-interference capability of capacitive liquid level detectors, Chinese patent application CN121089855A discloses a dynamic liquid level detection system and method based on a capacitive-photoelectric dual-mode sensor. This system, using a capacitive-photoelectric dual-mode sensor system and an adaptive weighted fusion algorithm, solves the problems of interference from temperature and liquid composition changes, as well as bubble interference, in liquid level detection. However, this approach introduces optical detection methods, increasing system complexity and cost.

[0007] In summary, existing capacitive liquid level detection technology still has the following problems: (1) Limited form and poor versatility: Sensors using rigid substrates cannot be attached to curved surfaces and can only be adapted to containers of specific sizes and shapes. Changing containers requires changing sensors, resulting in low flexibility. (2) The medium is sensitive and frequent calibration is required: Traditional schemes rely on the absolute value of capacitance at a single frequency to calculate the liquid level, which is highly sensitive to the dielectric constant of the liquid. Changing the medium will cause the calibration model to fail. (3) Large environmental interference, easy to cause drift: Interference factors such as fluctuations in ambient temperature and humidity, uneven container wall thickness and material differences will introduce uncontrollable parasitic capacitance, resulting in measurement drift; (4) It is difficult to balance the range and sensitivity of the sensor: Most of the existing flexible liquid level electrodes use single-structure interdigitated electrodes. Either they pursue high density and high sensitivity, resulting in a short measurement range, or they use wide-spacing long electrodes, resulting in low sensitivity. They cannot simultaneously meet the requirements of high sensitivity, wide range and high precision detection. Summary of the Invention

[0008] This invention provides a liquid level detection method, an interdigitated electrode structure, a liquid level sensor, and a medium, thereby solving at least one of the aforementioned technical problems.

[0009] To achieve the above objectives, this application proposes the following technical solution: A liquid level detection method, applicable to a liquid level sensor equipped with a dual-frequency excitation circuit, wherein the first frequency is less than the second frequency, includes: Obtain the actual measured capacitance value and liquid level height, as well as the reference capacitance value when the container is unloaded. Calculate the difference between the capacitance value of the first frequency signal and the capacitance value of the second frequency signal, and construct a mapping model between the liquid level height and the difference value. Obtain the reference capacitance value. If the change in the reference capacitance value exceeds the threshold range, then determine to update the mapping model. The updated mapping model is used to calculate the real-time liquid level value.

[0010] Furthermore, the difference values ​​include: ; In the formula, C diff This is the capacitance difference value. C ( f 1) The capacitance value measured under the first frequency signal. C empty ( f 1) is the reference capacitance value under no-load conditions at the first frequency signal. C ( f 2) The capacitance value measured under the second frequency signal. C empty ( f 2) is the reference capacitance value under no-load conditions at the second frequency signal.

[0011] Furthermore, the change in the reference capacitance value includes: the rate of change of the current reference capacitance value relative to the reference capacitance value of the reference electrode when the container is unloaded, as the drift rate; and the rate of change of the current reference capacitance value relative to the previous reference capacitance value.

[0012] Based on the same inventive concept, this application proposes an interdigitated electrode structure, comprising: The PET substrate has its bottom surface attached to the outer wall of the container to be tested, enabling non-contact measurement. The top surface of the PET substrate is sequentially integrated with a first electrode, a second electrode, and a ring electrode. The thickness of the PET substrate is less than 0.1 mm. The first and second electrodes are interdigitated electrodes used to acquire liquid level signals from the outer wall of the container under test. The width of the interdigitated fingers, the gap between adjacent interdigitated fingers, and the effective length of the first electrode are all smaller than those of the second electrode, while the number of interdigitated finger pairs is greater than that of the second electrode. The first electrode is used to acquire electrical signals of minute changes in the liquid level, while the measurement range of the second electrode is greater than that of the first electrode. The ring electrode serves as a reference electrode to compensate for environmental interference. Insulating layers are provided between the first electrode and the second electrode, and between the second electrode and the ring electrode, for insulation and isolation between the electrode layers. The insulating layer is a Parylene-C thin film.

[0013] Furthermore, the first electrode has 12 pairs, an interdigitated finger width of 0.3 mm, a gap distance of 0.2 mm between adjacent interdigitated fingers, and an effective length of 40 mm.

[0014] Furthermore, the second electrode has 4 pairs, an interdigitated finger width of 2 mm, a gap distance of 1.5 mm between adjacent interdigitated fingers, and an effective length of 70 mm.

[0015] Based on the same inventive concept, this application proposes a liquid level sensor, comprising: The interdigitated electrode structure described above is used to generate corresponding signals for different liquid levels and frequencies; A dual-frequency excitation circuit is used to output a first frequency signal and a second frequency signal to each electrode, so that the interdigital electrode structure generates corresponding signals of different frequencies; wherein, the first frequency is lower than the second frequency. The signal processing unit is used to acquire the sampling signal from the interdigital electrode structure; convert the acquired signal into a capacitance value and feed it back to the control unit. The control unit is used to control the signal switching and switching of the dual-frequency excitation circuit; to obtain the capacitance values ​​corresponding to different frequencies and different liquid levels; and to calculate the real-time liquid level value based on the mapping model between liquid level height and capacitance difference.

[0016] Furthermore, the control unit also includes: acquiring the reference capacitance value of the annular electrode; if the reference capacitance value is greater than a threshold, updating the coefficients of the mapping model, and using the updated mapping model to calculate the real-time liquid level value.

[0017] Furthermore, the control unit is an MCU.

[0018] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the liquid level detection method as described above.

[0019] The beneficial effects of this invention are: This invention discloses a liquid level detection method adapted to a liquid level sensor equipped with a dual-frequency excitation circuit, where the two frequencies are different. This application uses the capacitance values ​​of the dual-frequency signals output by the dual-frequency excitation circuit for differential calculation, suppressing interference from the dielectric constant of the medium, and balancing measurement accuracy, anti-interference, and response speed. Furthermore, it utilizes the reference capacitance value obtained from the reference electrode to set up a mapping model update mechanism, actively responding to the impact of environmental changes on the mapping model, expanding the dynamic range of liquid level detection, and improving the anti-interference, accuracy, and robustness of real-time detection, making it applicable to various situations in real-world scenarios.

[0020] The liquid level sensor proposed in this application uses a flexible substrate, making it adaptable to containers of different shapes and possessing versatility. This liquid level sensor is a non-invasive sensor that adheres to the outer wall of the container, detecting changes in the internal liquid without contact or immersion in the solution being measured. This device effectively reduces the risk of contamination and corrosion.

[0021] The interdigitated electrode structure proposed in this application comprises two interdigitated electrode layers (a first electrode and a second electrode) for acquiring electrical signals (liquid level signals) corresponding to the liquid level on the outer wall of the container under test. The first electrode, which is closer to the PET substrate, has a significantly higher aspect ratio than the second electrode. A higher interdigitated electrode density results in higher sensor sensitivity and response speed, allowing the first electrode to sensitively capture minute changes in the liquid level within the container and obtain the corresponding signals. The second electrode, being longer than the first electrode, can cover a larger area for acquiring signals related to changes in the liquid level.

[0022] In the interdigitated electrode structure of this application, the sensitive sensing and large-area coverage are designed as two layers of electrodes, which reduces the influence of stray capacitance / leakage current caused by the direct connection of the high-density interdigitated area (first electrode) to the external circuit, and improves the signal-to-noise ratio and measurement repeatability. At the same time, the large-area coverage (second electrode) increases the measurement range of the interdigitated electrode structure, and the low electrode density and low spacing of this layer facilitate subsequent lead assembly, reduce assembly difficulty, and improve signal stability.

[0023] This application integrates a ring electrode on the second electrode as a reference electrode to compensate for interference from ambient temperature, humidity, dielectric interference, etc., and improve the anti-interference capability of the interdigital electrode structure.

[0024] In this application, the insulating layer is a Parylene-C thin film with stepped coverage, which ensures the integrity and reliability of the insulating layer, eliminates the risk of local breakdown, and guarantees the signal stability of the interdigital electrode structure. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the interdigitated electrodes of this application; Figure 2 This is a schematic diagram of the reference electrode structure; Figure 3 This is a schematic diagram of the second electrode structure; Figure 4 This is a schematic diagram of the liquid level sensor of this application; Figure 5 This is a flowchart of the liquid level detection method of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising”, “including”, etc., as used herein indicate the presence of the said features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0028] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0029] like Figure 1 As shown, this application provides an interdigitated electrode structure, including: The PET substrate has its bottom surface attached to the outer wall of the container to be tested, enabling non-contact measurement. The top surface of the PET substrate is sequentially integrated with a first electrode, a second electrode, and a ring electrode. The thickness of the PET substrate is less than 0.1 mm.

[0030] The first and second electrodes are interdigitated electrodes used to acquire liquid level signals from the outer wall of the container under test. The width of the interdigitated fingers, the gap distance between adjacent interdigitated fingers, and the effective length of the first electrode are all smaller than those of the second electrode, while the number of interdigitated finger pairs is greater than that of the second electrode. The first electrode is used to acquire electrical signals of subtle changes in the liquid surface, while the measurement range of the second electrode is greater than that of the first electrode. The ring electrode serves as a reference electrode to compensate for environmental interference. Insulating layers are provided between the first and second electrodes, and between the second electrode and the ring electrode, for insulation and isolation between the electrode layers. The insulating layers are Parylene-C thin films.

[0031] Preferably, the PET substrate in this application has a thickness of 0.08 mm, which can be rolled up and adhered to the outer wall of a cylindrical container with a diameter of 8-30 mm.

[0032] Using PET (polyethylene terephthalate) as the base material for the interdigitated electrode structure results in low production costs, simple manufacturing processes, and good economic efficiency. Furthermore, the flexible electrode made of PET substrate can be fitted to both curved and non-curved containers, offering high flexibility.

[0033] Furthermore, the interdigitated electrode structure proposed in this application is attached to the outer wall of the container, allowing for the detection of internal liquid changes without contact or immersion in the solution to be tested. This device effectively reduces the risk of contamination and corrosion.

[0034] In this application, the insulating layer is a Parylene-C film. Parylene-C is a polymer film material produced by chemical vapor deposition of xylene dimers. The Parylene-C film is prepared by chemical vapor deposition, forming a dense film without pinholes or stress, with stepped coverage, ensuring the integrity and reliability of the insulating layer and eliminating the risk of localized breakdown.

[0035] like Figure 2 As shown, this application provides a schematic diagram of a ring electrode.

[0036] In this application, the ring electrode is made of copper ring with a width of 3 mm.

[0037] This application integrates a ring electrode on the second electrode as a reference electrode to compensate for interference from ambient temperature, humidity, dielectric interference, etc., and improve the anti-interference capability of the interdigital electrode structure.

[0038] The first electrode has 12 pairs, an interdigitated finger width of 0.3 mm, a gap distance of 0.2 mm between adjacent interdigitated fingers, and an effective length of 40 mm.

[0039] The second electrode has 4 pairs, an interdigitated finger width of 2 mm, a gap distance of 1.5 mm between adjacent interdigitated fingers, and an effective length of 70 mm.

[0040] like Figure 3 As shown, this application provides a schematic diagram of the second electrode to illustrate the relative relationships between the interdigitated finger width w, the gap distance s between adjacent interdigitated fingers, and the effective length l. In practical use, the effective length direction of the (interdigitated fingers) of the first and second electrodes is perpendicular to the direction of liquid level change.

[0041] The interdigitated electrode structure proposed in this application comprises two interdigitated electrode layers (a first electrode and a second electrode) for acquiring electrical signals (liquid level signals) corresponding to the liquid level on the outer wall of the container under test. The first electrode, which is closer to the PET substrate, has a significantly higher aspect ratio than the second electrode. A higher interdigitated electrode density results in higher sensor sensitivity and response speed, allowing the first electrode to sensitively capture minute changes in the liquid level within the container and obtain the corresponding signals. The second electrode, being longer than the first electrode, can cover a larger area for acquiring signals related to changes in the liquid level.

[0042] In the interdigitated electrode structure of this application, the sensitive sensing and large-area coverage are designed as two layers of electrodes, which reduces the influence of stray capacitance / leakage current caused by the direct connection of the high-density interdigitated area (first electrode) to the external circuit, and improves the signal-to-noise ratio and measurement repeatability. At the same time, the large-area coverage (second electrode) increases the measurement range of the interdigitated electrode structure, and the low electrode density and low spacing of this layer facilitate subsequent lead assembly, reduce assembly difficulty, and improve signal stability.

[0043] like Figure 4 As shown, based on the same inventive concept, this application provides a liquid level sensor, including: an interdigital electrode structure, a dual-frequency excitation circuit, a signal processing unit, and a control unit.

[0044] Preferably, the interdigitated electrode structure described above can be used to generate corresponding signals for different liquid levels and frequencies.

[0045] The dual-frequency excitation circuit is used to output a first frequency signal and a second frequency signal to each electrode, so that the interdigital electrode structure generates corresponding signals of different frequencies; wherein, the first frequency is less than the second frequency.

[0046] Preferably, the second frequency is 5-20 times that of the first frequency to avoid harmonic overlap. For example, the first frequency is 100kHz and the second frequency is 1MHz.

[0047] In this application, the dual-frequency excitation circuit is controlled by a control unit to switch the analog switches.

[0048] This application introduces high-frequency and low-frequency signals using a dual-frequency excitation circuit. The low-frequency signal identifies interference such as changes in the conductivity of the medium, ensuring measurement stability; the high-frequency signal captures real liquid level changes, improving response speed and detection resolution.

[0049] By combining high-frequency and low-frequency signal data processing, the influence of medium changes is eliminated, and the measurement accuracy, anti-interference and response speed are balanced, thus expanding the application range of liquid level sensors.

[0050] The signal processing unit is used to acquire the sampling signal from the interdigital electrode structure; convert the sampling signal into capacitance value and feed it back to the control unit.

[0051] Preferably, the signal processing unit includes a data acquisition chip and a capacitor-to-digital converter.

[0052] For example, the CAP1298 chip collects the capacitance signal, converts the capacitance signal into a digital value through a capacitance-to-digital converter, and transmits it to the control unit through the I²C interface.

[0053] Preferably, the signal acquisition can also be performed by the control unit.

[0054] The control unit is used to control the signal switching of the dual-frequency excitation circuit; to obtain the capacitance values ​​corresponding to different frequencies and liquid levels; and to calculate the real-time liquid level value based on the mapping model between liquid level height and capacitance difference.

[0055] The control unit also includes: acquiring the reference capacitance value of the annular electrode; if the reference capacitance value is greater than a threshold, updating the coefficients of the mapping model; and using the updated mapping model to calculate the real-time liquid level value.

[0056] Preferably, the control unit is an MCU, such as an ESP32-S3 or other chips.

[0057] Preferably, the liquid level sensor further includes a display unit for receiving and displaying the real-time liquid level value output by the control unit.

[0058] Preferably, the liquid level sensor can also be equipped with a host computer to receive the real-time liquid level value output by the control unit, which facilitates subsequent data processing and storage.

[0059] like Figure 5 As shown, this application also proposes a liquid level detection method applicable to liquid level sensors equipped with dual-frequency excitation circuits, wherein the first frequency is less than the second frequency, comprising: Obtain the actual measured capacitance value and liquid level height, as well as the reference capacitance value when the container is unloaded. Calculate the difference between the capacitance value of the first frequency signal and the capacitance value of the second frequency signal, and construct a mapping model between the liquid level height and the difference value. Obtain the reference capacitance value. If the change in the reference capacitance value exceeds the threshold range, determine to update the mapping model. Calculate the real-time liquid level value using the updated mapping model.

[0060] Based on the above-mentioned liquid level sensor, this application proposes its operating method as follows: After the liquid level measurement system is assembled and powered on, it collects the reference capacitance value of the container under no-load conditions. C empty .

[0061] The control unit controls the dual-frequency excitation circuit to apply low-frequency and high-frequency signals to the interdigitated electrode structure respectively, and obtains the reference capacitance value of the container under no-load conditions through the signal processing unit. C empty .in, C empty ( f 1 The value is the reference capacitance under no-load conditions at the first frequency signal. C empty ( f 2 ) is the reference capacitance value under no-load conditions under the second frequency signal.

[0062] The reference capacitance value of the container under no-load conditions is used as the zero-point reference for subsequent liquid level calculations to eliminate the influence of electrode parasitic capacitance, lead wire distributed parameters, and initial environmental interference.

[0063] Obtain the actual measured capacitance value and liquid level height. Based on the reference capacitance value, calculate the difference between the capacitance value of the first frequency signal and the capacitance value of the second frequency signal. C diff Construct a mapping model between liquid level height and difference value. h = α× C diff + β .

[0064] In the formula, α、β The coefficients of the mapping model are determined by data fitting using the actual measured liquid level height and the obtained capacitance value.

[0065] Preferably, the above mapping model can be a one-time relation or a multiple relation, and this application does not limit it.

[0066] The formula for calculating the difference is as follows:

[0067] In the formula, C diff The difference value, C ( f 1 The capacitance value is obtained under the first frequency signal.C empty ( f 1 The value is the reference capacitance under no-load conditions at the first frequency signal. C ( f 2 The capacitance value is obtained under the second frequency signal. C empty ( f 2 ) is the reference capacitance value under no-load conditions under the second frequency signal.

[0068] Capacitive level sensors utilize the difference in dielectric constant of the medium to change the equivalent capacitance, converting the liquid level height into a change in capacitance, which is then converted into the liquid level value through a detection circuit.

[0069] In capacitive level sensors, the capacitor... C The calculation principle is as follows: In a vacuum or in air C = ε 0 S / d ; In liquid level measurement scenarios, i.e. after filling with liquid medium, C = ε 0 ε r S / d In the formula, capacitance C The unit is F ; ε 0 This is the vacuum permittivity, typically 8.85 × 10⁻⁶. -12 F / m; S The effective facing area of ​​the electrode is expressed in m². 2 ; d The distance between the two plates is in meters (m). ε r It is the relative permittivity (the value varies depending on the liquid / medium).

[0070] The difference value has a normalization property for the liquid dielectric constant, indicating that the liquid level measurement system provided in this application can effectively suppress the influence of changes in the liquid dielectric constant based on the mapping model.

[0071] After the above process, a mapping model was obtained. In actual use, the control unit controls the dual-frequency excitation circuit to apply low-frequency and high-frequency signals to the interdigitated electrode structure, respectively, and obtains the capacitance value of different frequencies corresponding to each liquid level through the signal processing unit, and calculates the capacitance difference value of that liquid level.

[0072] This application also sets up operational steps for periodically updating the model to fit real-world scenarios and achieve highly robust liquid level detection.

[0073] This application determines whether environmental conditions have changed based on the reference capacitance value of the set reference electrode, in order to evaluate whether the current mapping model is applicable.

[0074] Specifically, if the change in the reference capacitance value exceeds the threshold range, the mapping model is updated.

[0075] There are multiple ways to calculate the change in the reference capacitance value.

[0076] The change in the reference capacitance value includes: the rate of change of the current reference capacitance value relative to the baseline reference capacitance value of the reference electrode when the container is unloaded, and the rate of change of the current reference capacitance value relative to the previous reference capacitance value. Other calculation methods may also be used, which are not limited herein.

[0077] This application uses the reference capacitance value of the reference electrode as a criterion for judging common-mode drift caused by temperature, humidity, and parasitic capacitance. The formula for calculating the drift rate is as follows:

[0078] In the formula, C ref0 C is the reference capacitance value of the reference electrode when the container is unloaded. ref This is the reference capacitance value for the reference electrode.

[0079] If the drift rate is greater than the threshold, it is determined that the environment has changed, and the model coefficients are refitted.

[0080] The threshold is determined based on the actual environment or set based on experience.

[0081] If the drift rate exceeds a certain value (such as ±3%, ±5%, etc.), it is considered an environmental change. The specific value is determined based on the actual situation.

[0082] Alternatively, the rate of change of the current reference capacitance value relative to the previous reference capacitance value can be calculated and used as a criterion. If the rate of change exceeds a certain value, it is considered an environmental change. This certain value can be 3%, 5%, or other values, serving as a threshold.

[0083] Preferably, the update frequency of the coefficients in the mapping model can be determined based on the rate of change of the monitored reference capacitance value; or an update cycle can be set and the update time fixed (such as 5 minutes, 3 minutes, etc.); or the update cycle can be set based on the change in liquid level; or other settings and adjustments can be made, which are not limited here.

[0084] Based on the above environmental assessment, the coefficients of the mapping model are updated using the real-time measured capacitance value and the reference capacitance value. The updated mapping model is then used to calculate the real-time liquid level value, thereby achieving highly robust real-time liquid level monitoring.

[0085] It should be noted that the above content only illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principles of the present invention, and all such improvements and modifications should be considered within the scope of protection of the claims of the present invention.

Claims

1. A liquid level detection method, characterized in that, Suitable for level sensors equipped with dual-frequency excitation circuits, where the first frequency is less than the second frequency, including: Obtain the actual measured capacitance value and liquid level height, as well as the reference capacitance value when the container is unloaded. Calculate the difference between the capacitance value of the first frequency signal and the capacitance value of the second frequency signal, and construct a mapping model between the liquid level height and the difference value. Obtain the reference capacitance value. If the change in the reference capacitance value exceeds the threshold range, then determine to update the mapping model. The updated mapping model is used to calculate the real-time liquid level value.

2. The liquid level detection method according to claim 1, characterized in that, Difference values, including: ； In the formula, C diff This is the capacitance difference value. C ( f 1) The capacitance value measured under the first frequency signal. C empty ( f 1) is the reference capacitance value under no-load conditions at the first frequency signal. C ( f 2) The capacitance value measured under the second frequency signal. C empty ( f 2) is the reference capacitance value under no-load conditions at the second frequency signal.

3. The liquid level detection method according to claim 1, characterized in that, The change in the reference capacitance value includes: the rate of change of the current reference capacitance value relative to the reference capacitance value of the reference electrode when the container is unloaded, which is used as the drift rate; and the rate of change of the current reference capacitance value relative to the previous reference capacitance value.

4. An interdigitated electrode structure, characterized in that, include: The PET substrate has its bottom surface attached to the outer wall of the container to be tested, enabling non-contact measurement. The top surface of the PET substrate is sequentially integrated with a first electrode, a second electrode, and a ring electrode. The thickness of the PET substrate is less than 0.1 mm. The first and second electrodes are interdigitated electrodes used to acquire liquid level signals from the outer wall of the container under test. The width of the interdigitated fingers, the gap between adjacent interdigitated fingers, and the effective length of the first electrode are all smaller than those of the second electrode, while the number of interdigitated finger pairs is greater than that of the second electrode. The first electrode is used to acquire electrical signals of minute changes in the liquid level, while the measurement range of the second electrode is greater than that of the first electrode. The ring electrode serves as a reference electrode to compensate for environmental interference; insulating layers are provided between the first electrode and the second electrode, and between the second electrode and the ring electrode, for insulation and isolation between the electrode layers. The insulating layer is a Parylene-C film.

5. The interdigitated electrode structure according to claim 4, characterized in that, The first electrode has 12 pairs, an interdigitated finger width of 0.3 mm, a gap distance of 0.2 mm between adjacent interdigitated fingers, and an effective length of 40 mm.

6. The interdigitated electrode structure according to claim 4, characterized in that, The second electrode has 4 pairs, an interdigitated finger width of 2 mm, a gap distance of 1.5 mm between adjacent interdigitated fingers, and an effective length of 70 mm.

7. A liquid level sensor, characterized in that, include: The interdigitated electrode structure as described in any one of claims 4-6 is used to generate corresponding signals at different liquid levels and frequencies; A dual-frequency excitation circuit is used to output a first frequency signal and a second frequency signal to each electrode, so that the interdigital electrode structure generates corresponding signals of different frequencies; wherein, the first frequency is lower than the second frequency. The signal processing unit is used to acquire the sampling signal from the interdigital electrode structure; convert the acquired signal into a capacitance value and feed it back to the control unit. The control unit is used to control the signal switching and switching of the dual-frequency excitation circuit; to obtain the capacitance values ​​corresponding to different frequencies and different liquid levels; and to calculate the real-time liquid level value based on the mapping model between liquid level height and capacitance difference.

8. The liquid level sensor according to claim 7, characterized in that, The control unit also includes: acquiring the reference capacitance value of the annular electrode; if the reference capacitance value is greater than a threshold, updating the coefficients of the mapping model; and using the updated mapping model to calculate the real-time liquid level value.

9. The liquid level sensor according to claim 7, characterized in that, The control unit is an MCU.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the liquid level detection method as described in any one of claims 1-3.

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