An autonomous measurement type capacitive water quantity sensor and detection method

Abstract

A self-measuring capacitive water volume sensor and its detection method are disclosed, comprising a circuit box assembly and a sensitive measurement unit. The circuit box assembly is connected to the sensitive measurement unit and consists of a signal acquisition board and a signal processing board. The signal acquisition board serves as the medium for the signal processing board to apply excitation signals to the sensitive measurement unit and to acquire feedback signals. The signal processing board is used for power conversion, sensor measurement functions, and communication with external devices. The sensitive measurement unit is used to measure the water level height and the dielectric constant of the liquid. The circuit box assembly of this invention measures the capacitance presented by the sensitive measurement unit and calculates it as the sensor's immersion height in water. A communication module is used for communication with external devices. A protection and isolation module is used to protect the external interface of the water volume sensor, enabling the water volume sensor to operate safely and reliably in complex electromagnetic environments and significantly suppressing and shielding electromagnetic interference signals generated by the product itself.

Description

Technical Field

[0001] This invention relates to the field of water volume sensor technology, and in particular to an autonomous measurement capacitive water volume sensor and its detection method. Background Technology

[0002] With rapid societal development and scientific and technological innovation, water volume sensor technology has permeated various fields, including industrial production, scientific research and development, fire fighting and rescue, and flood and drought control. Over the past few decades, researchers worldwide have made unremitting efforts, resulting in water volume sensors manufactured based on principles such as piezoresistive, ultrasonic, fiber optic, and photoelectric. Compared to other types of sensors, capacitive water volume sensors offer advantages such as good temperature stability, simple structure, and high sensitivity. However, typical capacitive water volume sensors rely on dedicated integrated capacitance measurement chips, and currently, there are no safe and controllable domestic alternatives for these chips. This results in water volume sensors lacking complete independent intellectual property rights, potentially impacting national security.

[0003] During normal use, impurities such as particulate matter and even microorganisms will inevitably accumulate on the surfaces of the inner and outer electrodes of the sensor's sensitive measuring unit. Furthermore, as the sensor's usage time increases, the amount of these accumulated particles may also increase, causing the capacitance value corresponding to the zero or full water level to deviate from the preset value. This necessitates calibrating the water sensor, which requires adding and draining water from the tank—a tedious and labor-intensive process that also wastes water resources. Additionally, fluctuations in water level and changes in liquid composition or concentration during use can affect the capacitance measurement results, leading to significant deviations between the sensor's readings and the actual true value. Summary of the Invention

[0004] The purpose of this invention is to provide an autonomous measurement capacitive water volume sensor and a water volume detection method to solve the problems of wasted water resources during calibration, instability caused by water level fluctuations, and the influence of changes in liquid composition or concentration on the capacitance measurement results, resulting in a large deviation between the sensor's measured results and the actual true value.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An autonomous measurement capacitive water level sensor includes a circuit box assembly and a sensitive measurement unit. The circuit box assembly is connected to the sensitive measurement unit and is divided into a signal acquisition board and a signal processing board. The signal acquisition board is the medium through which the signal processing board applies excitation signals to the sensitive measurement unit and acquires feedback signals. The signal processing board is used for power conversion, sensor measurement functions, and communication with external devices. The sensitive measurement unit is used to measure water level height and the dielectric constant of the liquid.

[0007] Furthermore, the sensitive measurement unit includes an outer tube, an inner tube, and a compensation tube. The outer tube and the inner tube are coaxially arranged, and the compensation tube is coaxially connected to the inner tube. The outer tube is grounded, the inner tube is used to measure the water level, and the compensation tube is used to measure the dielectric constant of the liquid.

[0008] Furthermore, fixed seats are provided at both ends of the outer tube, which are used to support and limit the inner and outer tubes and the compensation tube.

[0009] Furthermore, a protective sleeve is installed between the outer and inner tubes, which provides auxiliary support for both tubes; the protective sleeve is equipped with clamps to secure it.

[0010] Furthermore, the outer pipe is also equipped with upper and lower hanging clamps for connecting the water volume sensor to the side wall of the water tank.

[0011] Furthermore, the circuit box assembly includes a power supply unit, an excitation unit, a signal sampling unit, a processing unit, and a communication interface unit; the processing unit is connected to the excitation unit, the excitation unit is connected to the sensitive measurement unit, the sensitive measurement unit is connected to the signal sampling unit, and the signal sampling unit is connected to the processing unit, forming an excitation loop; the communication interface unit is connected to the processing unit, and the power supply unit is used to supply power to the excitation loop.

[0012] Furthermore, a detection method for an autonomous measurement capacitive water volume sensor includes the following steps:

[0013] The processing unit provides a local oscillator signal of a fixed frequency to the excitation unit;

[0014] The excitation unit generates a sinusoidal AC signal with the same frequency as the local oscillator signal and uses this signal as the excitation for the sensitive measurement unit;

[0015] The sensitive measurement unit uses the working principle of a capacitor to convert the water level height into the capacitance of the capacitor;

[0016] The signal sampling unit samples the feedback signal from the sensitive measurement unit, and the processing unit uses the lock-in amplification method to convert the feedback signal into a phase signal and calculates the corresponding capacitance value.

[0017] The processing unit retrieves the capacitance-water level calibration data table obtained in advance through experiments to obtain the water level value;

[0018] Real-time monitoring of changes in the dielectric constant of the liquid being measured compensates for the water level height measured by the product, eliminating the influence of changes in dielectric constant on the water level height measurement results;

[0019] The communication interface unit sends the calculated water level height value to the computer / control box.

[0020] Furthermore, the capacitance-water level calibration data table is a table showing the correspondence between normalized capacitance values ​​and water level heights, obtained through experimental calibration using any solution.

[0021] Furthermore, the processing unit monitors the capacitance of the inner tube and the compensation tube, records the maximum and minimum values ​​of the capacitance, and compares the maximum value with the capacitance value corresponding to the full water level in the capacitance-water level calibration data table. The maximum value after comparison is taken as the capacitance corresponding to the full water level. The minimum value is compared with the capacitance value corresponding to the zero water level in the capacitance-water level calibration data table. The minimum value after comparison is taken as the capacitance corresponding to the zero water level. The processing unit updates the capacitance values ​​corresponding to the full water level and zero water level in the capacitance-water level calibration data table with the maximum and minimum values ​​to achieve calibration of the full water level and zero water level.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] The circuit box assembly of this invention measures the capacitance presented by the sensitive measurement unit and calculates it as the immersion height of the sensor in water; the communication module is used for communication with external devices; the protection and isolation module is used to protect the external interface of the water sensor, so that the water sensor can not only work safely and reliably in complex electromagnetic environments, but also significantly suppress and shield the electromagnetic interference signals generated by the product itself.

[0024] This invention introduces a method for conversion and compensation based on "capacitance-water level". Based on the normalized capacitance value, a search is performed in the "capacitance-water level" database to obtain the current corresponding water level value, and the measured height value is unaffected by changes in the liquid's dielectric constant.

[0025] This invention monitors the capacitance of the inner tube and the compensation tube to determine when the water level is at zero or full, and then performs automatic calibration at that moment, avoiding the tedious operation of adding and draining water. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of an autonomous measurement capacitive water volume sensor provided in an embodiment of this application;

[0027] Among them: circuit box assembly 101, sensitive measurement unit 102, fixing base 103, protective sleeve 104, clamp 105, upper hanging clamp 106, lower hanging clamp 107;

[0028] Figure 2 Schematic diagram of the structure of the sensitive measurement unit;

[0029] Among them, the upper tube 201, the outer tube 202, and the compensation tube 203 are excitation units that apply independent excitation signals to the two tubes respectively.

[0030] Figure 3 A schematic diagram illustrating the working principle of an autonomous measurement capacitive water volume sensor provided in this application embodiment;

[0031] Among them, there are 301 power supply unit, 302 excitation unit, 303 composite sensitive measurement unit, 304 signal sampling unit, 305 processing unit, and 306 communication interface unit.

[0032] Figure 4 A schematic diagram illustrating the acquisition principle of the feedback signal from the sensitive measurement unit provided in this application embodiment;

[0033] Figure 5 This is a flowchart of a water quantity detection method provided in an embodiment of this application. Detailed Implementation

[0034] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0035] This invention relates to the field of water volume sensor technology, and in particular to a self-measuring capacitive water volume sensor and its detection method. This self-measuring capacitive water volume sensor comprises: a circuit box assembly, an inner tube, an outer tube, a compensation tube, a mounting base, a protective sleeve, clamps, and mounting brackets. This invention introduces a feedback resistor into the excitation circuit of the capacitor, and by acquiring the potential across the feedback resistor, the capacitance value presented by the capacitor can be obtained. Furthermore, there is a unique correspondence between the sensor's immersion height and its capacitance. By measuring and calculating the presented capacitance value, water volume information can be obtained in real time. Simultaneously, it can monitor changes in the dielectric constant of the measured liquid in real time and compensate for the measured water level height according to a certain algorithm, thereby eliminating the influence of dielectric constant changes on the water level height measurement results. This invention also features information transmission, resistance to water surface disturbance, and zero / full water level calibration without the need for adding or draining water, satisfying both the requirements for water level measurement and accuracy, greatly improving the efficiency of water volume detection.

[0036] Figure 1 This application provides a schematic diagram of a self-measuring capacitive water volume sensor structure, as shown in the embodiments below. Figure 1 As shown, the self-measuring capacitive water volume sensor includes a circuit box assembly 101, a sensitive measurement unit 102, a mounting base 103, a protective sleeve 104, a clamp 105, an upper hanging clamp 106, and a lower hanging clamp 107. Among them:

[0037] The circuit box assembly 101 is divided into a signal acquisition board and a signal processing board. The signal acquisition board is the medium through which the signal processing board applies excitation signals to the sensitive measurement unit and acquires feedback signals. The signal processing board performs the following functions: power conversion, sensor measurement, communication with external devices, and self-testing.

[0038] like Figure 2 As shown, the composite sensitive measurement unit 102 includes an outer tube 201, an inner tube 202, and a compensation tube 203. The outer tube 201, inner tube 202, and compensation tube 203 are ring-shaped and are coaxial at the bottom. The outer tube 201 is grounded, the inner tube 202 is used to measure the water level, and the compensation tube 203 is used to measure the dielectric constant of the liquid.

[0039] In this embodiment, Teflon powder coating is used to insulate the entire inner tube.

[0040] Furthermore, the fixing seat 103 supports and limits the inner and outer tubes and the compensation tube to ensure that the three meet the coaxiality requirements at the bottom; the protective sleeve 104 provides auxiliary support for the inner and outer tubes to enhance their coaxiality. The protective sleeve is installed in close contact with the outer surface of the outer tube. Multiple protective sleeves are used in combination to ensure the coaxiality of the inner and outer tubes, thereby structurally ensuring the required measurement accuracy of the sensor. The clamp 105 is used to fix the protective sleeve; the mounting bracket is used to connect the water volume sensor to the side wall of the water tank. In this embodiment, the mounting bracket is divided into two parts: an upper bracket 106 and a lower bracket 107. The upper bracket is fixed to the circuit box, and the lower bracket is composed of two semicircles that contact the outer tube of the product through the protective sleeve.

[0041] like Figure 3 As shown, in terms of working principle, the water sensor can be divided into a power supply unit 301, an excitation unit 302, a composite sensitive measurement unit 303, a signal sampling unit 304, a processing unit 305, and a communication interface unit 306. The processing unit 305 introduces a feedback resistor into the excitation circuit of the composite sensitive measurement unit 303. The potential at the front end of the feedback resistor is the excitation signal, and the potential at the back end has a certain physical relationship with the capacitance value presented by the capacitor. By acquiring the potential across the feedback resistor, the capacitance value presented by the capacitor can be obtained.

[0042] The acquisition principle of the feedback signal of the sensitive measurement unit is as follows: Figure 4 As shown in the figure, To process the sinusoidal excitation signal applied by the processing unit to the sensitive measurement unit, R m For the feedback resistor, C p R is the capacitance presented by the sensitive measurement unit. p To be with C p Equivalent resistance in parallel. C pIt is a mapping of the submersion height of the sensitive measuring unit in water, R p It can reflect the quality of the liquid being tested to a certain extent. By measuring R... m Back-end potential signal The capacitance C presented by the sensitive measurement unit can then be obtained. p and resistance R p .

[0043] In some embodiments, the feedback resistor R is controlled by a follower circuit and an ADC integrated in the microprocessor. m The voltage signals at both ends are sampled, and after filtering out white noise and low-frequency interference signals, the amplitude and phase of the sampled signal are calculated by a lock-in amplifier composed of a digital mixer module and a Butterworth filter.

[0044] Figure 5 A flowchart of a water volume detection method provided in this application embodiment can be applied to the self-measuring capacitive water volume sensor in the above embodiments. The method includes at least the following steps:

[0045] Step S001: The processing unit provides a local oscillator signal of fixed frequency to the excitation unit.

[0046] Step S002: The excitation unit generates a sinusoidal AC signal with the same frequency as the local oscillator signal, and uses this signal as the excitation for the sensitive measurement unit (coaxial cylindrical capacitor).

[0047] To control and improve the measurement accuracy of the water level sensor, the excitation signal and the local oscillator signal must be of the same frequency and phase, or have the same frequency but a fixed phase difference. For example, the excitation signal can be generated using sinusoidal pulse width modulation filtering, square wave low-pass filtering, or digital-to-analog conversion. In some embodiments, square wave low-pass filtering is used to generate a single-ended square wave with a frequency of 5.12 kHz and an amplitude of 5 V through an excitation signal generator. This square wave is then filtered and attenuated to generate a unipolar sinusoidal signal of the same frequency, with a phase delay and an amplitude slightly attenuated from 5 V. This sinusoidal signal will be used as the excitation signal for the sensitive measurement unit (coaxial cylindrical capacitor).

[0048] Step S003: The sensitive measurement unit uses the working principle of a capacitor to convert the water level height into the capacitance of the capacitor;

[0049] In one embodiment, the water level sensor is installed perpendicular to the water surface inside the water tank. The inner and outer electrodes are the positive and negative plates of a capacitor, and a certain gap needs to be maintained between them. The medium between the two plates includes both water and air. The capacitance of the capacitor is equal to the sum of the capacitances of these two parts. The increase in capacitance when there is water in the tank changes linearly with the water level, thus converting the measurement of water level into a measurement of capacitance.

[0050] Step S004: The signal sampling unit samples the feedback signal from the sensitive measurement unit, and the processing unit uses the lock-in amplification method to convert the feedback signal into a phase signal and calculates the corresponding capacitance value.

[0051] The sampling of the voltage across the feedback resistor is achieved using a follower circuit. It is important to note that the amplifiers selected in the follower circuit for sampling the voltage across the feedback resistor are two sets from the same chip to ensure the consistency of physical characteristics to the greatest extent possible, thereby maximizing the measurement accuracy.

[0052] Step S005: The processing unit retrieves the "capacitance-water level height" calibration data table obtained in advance through experiments to obtain the water level height value;

[0053] The dry capacitance C of the inner and outer tubes when there is no water in the water tank. P0 The dry capacitance C presented by the compensation tube and the outer tube S0 This can be obtained through actual measurement; therefore, for a water sensor of a certain length, its dry capacitance C can be determined. P0 and C S0 It is considered a constant value. The normalized capacitance value C is defined. r for Where C P C is the capacitance between the inner and outer tubes. S To compensate for the capacitance between the outer tube and the inner tube, C P0 C is the dry capacitance between the inner and outer tubes when there is no water in the water tank. S0 To compensate for the dry capacitance presented by the outer tube and the inner tube, the normalized capacitance value C is... r The capacitance-water level height (h) is independent of the dielectric constant and has a unique correlation with the water level height (h). Any solution (or any fluid dielectric) can be used, and the capacitance-water level height can be obtained through experimental calibration. In actual operation, when the water surface is at a certain height, the capacitance presented by the inner tube and the compensation tube can be measured and calculated separately. The normalized capacitance value is then calculated, and the current water level height is obtained by searching the capacitance-water level height calibration data table based on the normalized capacitance value. Furthermore, the measured height value is unaffected by changes in the liquid's dielectric constant.

[0054] Step S006: Monitor the change in dielectric constant of the liquid being measured in real time, and compensate for the water level height measured by the product according to a certain algorithm, thereby eliminating the influence of the change in dielectric constant on the water level height measurement result.

[0055] Step S007: The communication interface unit sends the water level height value calculated by the processing unit to the computer / control box.

[0056] In one embodiment, communication with external devices is achieved through a UART (Universal Asynchronous Receiver / Transmitter) interface and an SPI (Serial Peripheral Interface) interface. For example, the measured water level and sensor operating status information can be framed according to the ARINC-429 bus protocol specification and sent to the 429 protocol and driver chip via the microprocessor's SPI module. Simultaneously, to meet debugging needs, the water level, capacitance calculation information of the sensitive measuring unit, necessary intermediate variables during the calculation process, and sensor status information can be framed according to a specific frame format and sent to the 422 driver chip via the microprocessor's UART module.

[0057] This application also provides a method for calibrating zero or full water levels without adding or draining water. During normal use, the sensor can monitor the capacitance presented by the compensation tube and the inner tube to determine when the water level is at zero or full, and then perform autonomous calibration without adding or draining water at that moment.

[0058] During operation, the maximum capacitance value is recorded and compared with the capacitance value corresponding to the full water level in the "Capacitance-Water Level Height" database. The larger value is taken as the capacitance corresponding to the full water level. The processing unit updates the capacitance value corresponding to the full water level in the "Capacitance-Water Level Height" database using this maximum value, thus achieving full water level calibration. If the capacitance shown by the compensation tube of the sensitive measuring unit decreases sharply, it indicates that the medium between the inner and outer tubes is entirely air. In this case, the capacitance shown by the inner tube is the capacitance corresponding to the zero water level. The processing unit measures, calculates, and records this capacitance and updates the capacitance value corresponding to the zero water level in the "Capacitance-Water Level Height" database, thus achieving zero-level calibration.

[0059] This application provides a method for resisting water surface disturbance. A rough surface treatment is applied to the sensitive measuring end faces of the cylindrical capacitor (i.e., the outer surface of the inner tube and the inner surface of the outer tube) to enhance the damping of fluid disturbance between the tubes, while minimizing the radial distance between the inner and outer tubes. A software filtering method is used to digitally filter the measured water level height sequence to reduce the impact of water surface disturbance; for example, a Kaiser-Bessel window function can be used as the filtering algorithm.

Claims

1. A detection method for a self-measuring capacitive water volume sensor, characterized in that, This method is based on a self-measuring capacitive water volume sensor, which includes a circuit box assembly (101) and a sensitive measurement unit (102). The circuit box assembly (101) is connected to the sensitive measurement unit (102). The circuit box assembly (101) is divided into a signal acquisition board and a signal processing board. The signal acquisition board is the medium through which the signal processing board applies excitation signals to the sensitive measurement unit and acquires feedback signals. The signal processing board is used for power conversion, sensor measurement functions, and communication with external devices. The sensitive measurement unit (102) is used to measure the water level height and the dielectric constant of the liquid. 101) includes a power supply unit (301), an excitation unit (302), a signal sampling unit (304), a processing unit (305), and a communication interface unit (306); the processing unit (305) is connected to the excitation unit (302), the excitation unit (302) is connected to the sensitive measurement unit (102), the sensitive measurement unit (102) is connected to the signal sampling unit (304), and the signal sampling unit (304) is connected to the processing unit (305), forming an excitation loop; the communication interface unit (306) is connected to the processing unit (305), and the power supply unit (301) is used to supply power to the excitation loop; The method includes the following steps: The processing unit (305) provides a local oscillator signal of a fixed frequency to the excitation unit (302); The excitation unit (302) generates a sinusoidal AC signal with the same frequency as the local oscillator signal and uses the signal as the excitation for the sensitive measurement unit (102); The sensitive measurement unit (102) uses the working principle of a capacitor to convert the water level height into the capacitance of the capacitor; The signal sampling unit (304) samples the feedback signal from the sensitive measurement unit (102), and the processing unit (305) uses the lock-in amplification method to convert the feedback signal into a phase signal and calculates the corresponding capacitance value. The processing unit (305) retrieves the capacitance-water level height calibration data table obtained in advance through experiments to obtain the water level height value; Real-time monitoring of changes in the dielectric constant of the liquid being measured compensates for the water level height measured by the product, eliminating the influence of changes in dielectric constant on the water level height measurement results; The communication interface unit (306) sends the water level height value to the computer / control box. The processing unit (305) calculates the water level height value.

2. The detection method of the self-measuring capacitive water volume sensor according to claim 1, characterized in that, The sensitive measurement unit (102) includes an outer tube (202), an inner tube (201) and a compensation tube (203). The outer tube (202) and the inner tube (201) are coaxially arranged, and the compensation tube (203) is coaxially connected to the inner tube (201). The outer tube (202) is grounded. The inner tube is used to measure the water level height, and the compensation tube is used to measure the dielectric constant of the liquid.

3. The detection method of the self-measuring capacitive water volume sensor according to claim 2, characterized in that, The outer tube (202) is provided with fixing seats (103) at both ends. The fixing seats (103) are used to support and limit the inner and outer tubes and the compensation tube.

4. The detection method of the self-measuring capacitive water volume sensor according to claim 2, characterized in that, A protective sleeve (104) is provided between the outer tube (202) and the inner tube (201). The protective sleeve (104) provides auxiliary support for the inner and outer tubes. A clamp (105) is provided on the protective sleeve (104). The clamp (105) is used to fix the protective sleeve.

5. The detection method of the self-measuring capacitive water volume sensor according to claim 2, characterized in that, The outer tube (202) is also equipped with an upper hanger (106) and a lower hanger (107) for connecting the water volume sensor to the side wall of the water tank.

6. The detection method of the self-measuring capacitive water volume sensor according to claim 1, characterized in that, The capacitance-water level calibration data table is a table showing the correspondence between normalized capacitance values ​​and water level heights. It is obtained through experimental calibration using any solution.

7. The detection method of the self-measuring capacitive water volume sensor according to claim 2, characterized in that, The processing unit monitors the capacitance of the inner tube and the compensation tube, records the maximum and minimum values ​​of the capacitance, and compares the maximum value with the capacitance value corresponding to the full water level in the capacitance-water level calibration data table. The maximum value is taken as the capacitance corresponding to the full water level. The minimum value is compared with the capacitance value corresponding to the zero water level in the capacitance-water level calibration data table. The minimum value is taken as the capacitance corresponding to the zero water level. The processing unit updates the capacitance values ​​corresponding to the full water level and zero water level in the capacitance-water level calibration data table with the maximum and minimum values ​​to achieve the calibration of the full water level and zero water level.

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