An ultrasonic liquid level detection method and system

Abstract

The application provides an ultrasonic liquid level detection method and system, applied to a container, the bottom of the container is at least partially composed of a metal wall, comprising the following steps: outputting an excitation signal to drive an ultrasonic probe arranged outside the metal wall to emit ultrasonic waves to the inside of the container, the ultrasonic waves propagate in a liquid medium in the container after penetrating the metal wall; obtaining echo electric signals received by the ultrasonic probe, and processing the echo electric signals to obtain level signals representing echo intensity; performing analog-digital conversion sampling on the level signals to obtain amplitude data; comparing the amplitude data with a preset threshold value, and determining whether an effective echo is received based on the comparison result; when it is determined that an effective echo is received, obtaining liquid level height information according to the time difference between the emitted ultrasonic waves and the received effective echo and the propagation speed of the ultrasonic waves in the liquid medium. The application improves the accuracy and reliability of liquid level detection.

Description

Technical Field

[0001] This application belongs to the field of electrical technology, specifically relating to an ultrasonic liquid level detection method and system. Background Technology

[0002] Liquid level detection is a fundamental technical requirement in container-type equipment. Accurately obtaining the liquid level information within the container is crucial for the safe operation and functional control of the equipment. Ultrasonic testing methods, due to their advantages of being non-contact, having a fast response speed, and offering high safety, are increasingly being introduced into the field of liquid level detection.

[0003] Currently, common liquid level detection methods include float switch type, electrode type, optical type, and pressure sensor type. The float switch type detects liquid level by triggering a switch through the rise and fall of a float, but its mechanical parts are prone to wear and jamming due to prolonged immersion in liquid. The electrode type utilizes the conductivity of water for detection, but the electrodes are susceptible to electrolytic corrosion in liquid environments. The optical type relies on the difference in refractive index of light in different media, but its light-transmitting window is easily covered by contaminants, leading to failure. The pressure sensor type indirectly calculates the liquid level by detecting the pressure of the liquid at the bottom, but changes in liquid density with temperature introduce significant errors. All of the above methods require the installation of detection components inside or on the inner wall of the container, resulting in complex structures and the risk of liquid contamination. Therefore, some solutions attempt to apply ultrasonic detection technology to container liquid level measurement, utilizing the characteristics of ultrasonic waves propagating in the medium and reflecting at interfaces to achieve non-contact detection. For example, CN218683751U discloses an ultrasonic water level sensing device for a tea container, including a container and a sensing device. The container wall has an installation area, and the sensing device is a flat ultrasonic sensor located in the installation area. The ultrasonic sensor is connected to a control device. The container has a first water level and at least one second water level. The first water level is used to detect the lowest water level in the container, and the second water level is used to detect a predetermined water level in the container. The ultrasonic sensor acquires the first water level and the second water level through ultrasonic waves and sends them to the control device.

[0004] However, existing ultrasonic liquid level detection solutions still have many shortcomings in practical applications. During the propagation of ultrasound, various interference signals are inevitably introduced, such as multiple reflections from the container wall, scattering signals caused by bubbles or suspended matter in the liquid, and environmental electromagnetic noise. These interference signals are mixed with the liquid surface echo signal, making it difficult to meet the reliability and accuracy requirements of automated equipment for liquid level detection. Summary of the Invention

[0005] This application provides an ultrasonic liquid level detection method and system, which can at least solve the technical problem that ultrasonic waves inevitably introduce various interference signals during propagation, such as multiple reflection signals from the container wall, scattering signals caused by bubbles or suspended matter in the liquid, and environmental electromagnetic noise. These interference signals are mixed with the liquid surface echo signal, making it difficult to meet the reliability and accuracy requirements of automated equipment for liquid level detection.

[0006] The technical solution of this application is as follows: On one hand, an ultrasonic liquid level detection method is provided, applied to a container, wherein the bottom of the container is at least partially composed of a metal wall, comprising the following steps: An excitation signal is output to drive an ultrasonic probe located on the outside of the metal wall to emit ultrasonic waves into the container. The ultrasonic waves penetrate the metal wall and propagate in the liquid medium inside the container. The echo electrical signal received by the ultrasonic probe is acquired, and the echo electrical signal is processed to obtain a level signal characterizing the echo intensity; The amplitude data is obtained by performing analog-to-digital conversion on the level signal; The amplitude data is compared with a preset threshold, and a valid echo is determined based on the comparison result. When a valid echo is received, the liquid level information is obtained based on the time difference between the transmission of the ultrasonic wave and the reception of the valid echo, and the propagation speed of the ultrasonic wave in the liquid medium.

[0007] The method provided in this application embodiment can achieve liquid level detection without opening holes in the inner wall of the container, avoiding problems such as water leakage, scaling, and corrosion caused by traditional hole-opening detection methods; at the same time, by using threshold comparison to identify effective echoes, it can effectively eliminate interference from noise and noise, thereby improving the accuracy and reliability of liquid level detection.

[0008] In one optional implementation, processing the echo electrical signal to obtain a level signal characterizing the echo intensity includes: The echo signal is amplified, and the amplified signal is rectified and filtered to output a DC level signal characterizing the echo intensity. The amplification factor for amplifying the echo electrical signal is 50 to 5000 times.

[0009] This implementation converts weak echo AC signals into easily sampled DC level signals through a three-stage signal processing link of amplification, rectification, and filtering, significantly improving the detectability and sampling stability of the echo signals. At the same time, by limiting the amplification factor to the range of 50 to 5000 times, it ensures sufficient amplification of weak signals while avoiding excessive amplification that introduces noise, thus ensuring reasonable gain allocation in the signal conditioning link and improving the signal-to-noise ratio and detection accuracy of the detection system.

[0010] In one optional embodiment, the effective echo is the echo of the ultrasonic wave returning to the ultrasonic probe after being reflected by the liquid surface in the container; The time difference is the duration between the start time of transmitting the ultrasonic wave and the start time of receiving the first valid echo.

[0011] This implementation defines the effective echo as the liquid surface reflection echo and the time difference as the duration between the start of the transmission and the start of the first effective echo. This provides an accurate time reference for subsequent liquid level calculations, avoids calculation deviations caused by using incorrect echo signals, and ensures the accuracy and consistency of the liquid level detection results.

[0012] In one alternative implementation, it further includes: Obtain the temperature of the medium inside the container; The propagation speed of the ultrasonic wave in the liquid medium is compensated and corrected based on the medium temperature, and the liquid level height information is calculated using the corrected sound speed.

[0013] This implementation eliminates the influence of water temperature changes on the propagation speed of ultrasonic waves by introducing a temperature sensor to detect the medium temperature in real time and dynamically compensate for the sound velocity. This allows the liquid level detection to maintain high accuracy across the entire temperature range from cold water to boiling, making it particularly suitable for household appliances such as kettles that operate in a wide temperature range. The temperature compensation is based on real-time correction according to physical principles rather than simple table lookup, and features good continuity and high accuracy.

[0014] In one optional embodiment, the excitation signal is boosted to a preset driving voltage via a driving circuit to drive the ultrasonic probe; The preset driving voltage ranges from 10V to 200V, and the frequency range of the ultrasonic waves generated by the ultrasonic probe ranges from 0.1MHz to 10MHz.

[0015] This embodiment ensures that the ultrasonic probe can generate sufficient energy to penetrate the metal wall by limiting the driving voltage range and the ultrasonic frequency range, while taking into account the balance between detection resolution and signal attenuation, so that the detection method can be adapted to the bottom of containers with different wall thicknesses and materials.

[0016] In one optional implementation, each step is repeated at a predetermined period to obtain continuous liquid level detection results, and the liquid level height information obtained from multiple consecutive detections is filtered and then the final liquid level signal is output. A control signal is generated based on the liquid level information. The control signal is used to perform at least one of the following control operations: anti-dry burning protection, quantitative water injection control, water level reminder, or automatic heating stop.

[0017] By periodically detecting and filtering, random errors and transient interference in a single detection are effectively suppressed, significantly improving the stability and smoothness of the detection results. At the same time, by combining the liquid level detection results with the intelligent control of the whole machine, multiple practical functions such as anti-dry burning protection, quantitative water injection, water level reminder, and automatic heating stop are realized, expanding the application value of the liquid level detection solution and improving the intelligence level and safety of the product.

[0018] On the other hand, an ultrasonic liquid level detection system is provided for use in a container, wherein the bottom of the container is at least partially composed of a metal wall, comprising: An ultrasonic probe, located on the outside of the metal wall, is used to emit ultrasonic waves into the container and receive the ultrasonic echoes reflected back from the liquid surface, converting the echoes into electrical signals. A driving circuit, electrically connected to the ultrasonic probe, is used to receive excitation signals and drive the ultrasonic probe to emit ultrasonic waves. The signal conditioning circuit, electrically connected to the ultrasonic probe, is used to amplify, rectify, and filter the electrical signal to output a DC level signal characterizing the echo intensity. An analog-to-digital converter circuit, connected to the signal conditioning circuit, is used to sample the level signal and convert it into amplitude data; The control unit, connected to the drive circuit and the analog-to-digital conversion circuit respectively, is used to output the excitation signal, compare the amplitude data with a preset threshold and determine whether a valid echo is received based on the comparison result. When it is determined that a valid echo is received, the liquid level height information is calculated based on the time difference between the emitted ultrasonic wave and the received valid echo and the propagation speed of the ultrasonic wave in the liquid medium.

[0019] In this embodiment, the system and method, corresponding to the independent claims, construct a complete hardware implementation architecture. The functions of each circuit module are clearly defined and work together to fully realize the above-mentioned liquid level detection method. The system adopts a modular design with clear interfaces between each unit, facilitating integration and layout on the circuit board of the home appliance. The ultrasonic probe adopts an integrated transceiver design, reducing the number of probes and installation complexity, and lowering system costs. The signal conditioning circuit uses a rectification and filtering scheme to convert the high-frequency echo signal into a DC level signal, making subsequent analog-to-digital conversion and threshold comparison simpler and more reliable.

[0020] In one alternative embodiment, the metal wall of the container is a thin-walled stainless steel bottom, and the ultrasonic probe is attached to the outside of the thin-walled stainless steel bottom by a high-temperature resistant coupling adhesive. The acoustic impedance of the high-temperature resistant coupling adhesive is between the acoustic impedance of the ultrasonic probe and the acoustic impedance of the thin-walled stainless steel bottom, and the thermal resistance of the high-temperature resistant coupling adhesive is configured to prevent heat from the bottom of the pot from being transferred to the ultrasonic probe.

[0021] The embodiments of this application use thin-walled stainless steel as the material for the bottom of the pot, which takes into account both thermal conductivity and sound wave penetration performance; the acoustic impedance matching design of the coupling adhesive greatly improves the transmission efficiency of ultrasonic waves from the probe to the bottom of the pot, solving the problem of sound energy attenuation caused by acoustic impedance mismatch; the thermal resistance characteristics of the coupling adhesive effectively isolate the heat conduction of the probe by the high temperature of the bottom of the pot, protecting the reliability of the probe in high-temperature working environments.

[0022] In one optional embodiment, the container is an electric kettle, which further includes a heating plate disposed below the bottom of the thin-walled stainless steel kettle. The heating plate has a perforated hole through which the ultrasonic probe passes, and the ultrasonic probe is installed on the outside of the bottom of the thin-walled stainless steel kettle through the perforated hole. The system also includes an auxiliary pressing plate and a fixing component. The auxiliary pressing plate is pressed onto the side of the ultrasonic probe away from the bottom of the pot, and the fixing component fixes the auxiliary pressing plate to the heating plate or the bottom structure of the pot, so as to press the ultrasonic probe tightly against the bottom of the pot and expel air during the curing process of the coupling adhesive.

[0023] The ultrasonic probe can be placed as close as possible to the bottom of the pot, avoiding the extension of the sound propagation path and energy attenuation caused by the thickness of the heating plate; at the same time, since the perforation is opened in the non-heated area, the temperature of the probe's working environment is relatively low, which further facilitates heat dissipation and extends the probe's lifespan.

[0024] In one optional embodiment, a temperature sensor is further included, connected to the control unit, for detecting the temperature of the medium inside the container and feeding back a temperature signal to the control unit; The control unit compensates and corrects the propagation speed of the ultrasonic wave in the liquid medium based on the temperature signal, and uses the corrected sound speed to calculate the liquid level information.

[0025] The temperature sensor provides accurate temperature data for temperature compensation, enabling the system to dynamically adjust the sound velocity parameter based on the real-time water temperature. This eliminates detection errors caused by temperature changes and ensures high accuracy of liquid level detection throughout the entire boiling process.

[0026] The method provided in this application embodiment can achieve liquid level detection without opening holes in the inner wall of the container, avoiding problems such as water leakage, scaling, and corrosion caused by traditional hole-opening detection methods; at the same time, by using threshold comparison to identify effective echoes, it can effectively eliminate interference from noise and noise, thereby improving the accuracy and reliability of liquid level detection. Attached Figure Description

[0027] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0028] Figure 1 A schematic diagram of the ultrasonic liquid level detection method is shown.

[0029] Figure 2 A schematic diagram is shown of an electric kettle simulating an ultrasonic probe.

[0030] Figure 3 A basic block diagram of an ultrasonic liquid level detection system is shown.

[0031] Figure 4 A schematic diagram of an ultrasonic probe mounted on the bottom of a kettle is shown.

[0032] Ultrasonic probe-1, pot bottom-2, auxiliary pressing plate-3, heating plate-4. Detailed Implementation

[0033] Embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0034] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0035] The technical solution of this application will be described in detail below with reference to specific application scenarios. The technical solution of this application can be applied to various household appliances that require detection of liquid levels within containers, especially suitable for liquid heating containers with metal bottoms, such as kettles and electric kettles. Taking an electric kettle as an example, when using a kettle to boil water, users need to monitor the water level in real time to avoid dry boiling or overflow during filling. Simultaneously, during the boiling process, the water level changes due to boiling and evaporation, requiring dynamic monitoring. This application uses an ultrasonic probe placed on the outside of the kettle bottom. It utilizes the principle that ultrasonic waves penetrate the metal bottom, propagate in the water, and are reflected by the liquid surface to detect the liquid level. This eliminates the need for openings in the inner wall of the kettle, maintaining its integrity and cleanliness, and avoiding problems such as leakage, scaling, and corrosion caused by openings and installing probes in traditional detection methods.

[0036] Ultrasonic waves propagate at a constant speed in a homogeneous medium, but are reflected when they encounter an interface between different media (such as the interface between water and air). This application utilizes this physical property by placing an ultrasonic probe on the outer side of the container's bottom. The ultrasonic wave penetrates the metal bottom from bottom to top, enters the liquid medium, and is reflected back to the probe after reaching the liquid surface. Since the distance between the ultrasonic probe and the liquid surface determines the round-trip time of the ultrasonic wave, the liquid level can be calculated by measuring the time difference between the emitted ultrasonic wave and the received echo. Simultaneously, because the propagation speed of ultrasonic waves in a liquid medium changes with temperature, this application also introduces a temperature compensation mechanism to correct the sound velocity based on the real-time water temperature to ensure detection accuracy.

[0037] The technical solutions defined in each claim of this application are described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Please see Figure 1 This application provides an ultrasonic liquid level detection method M100, applied to a container, the bottom of which is at least partially composed of a metal wall, comprising the following steps: Step S1: Output an excitation signal to drive the ultrasonic probe set on the outside of the metal wall to emit ultrasonic waves into the container. The ultrasonic waves penetrate the metal wall and propagate in the liquid medium inside the container.

[0039] Step S2: Acquire the echo electrical signal received by the ultrasound probe and process the echo electrical signal to obtain a level signal characterizing the echo intensity.

[0040] Step S3: Perform analog-to-digital conversion on the level signal to obtain amplitude data.

[0041] Step S4: Compare the amplitude data with the preset threshold, and determine whether a valid echo has been received based on the comparison result.

[0042] Step S5: When it is determined that a valid echo has been received, the liquid level height information is obtained based on the time difference between the emitted ultrasonic wave and the received valid echo, and the propagation speed of the ultrasonic wave in the liquid medium.

[0043] The method provided in this application embodiment can achieve liquid level detection without opening holes in the inner wall of the container, avoiding problems such as water leakage, scaling, and corrosion caused by traditional hole-opening detection methods; at the same time, by using threshold comparison to identify effective echoes, it can effectively eliminate interference from noise and noise, thereby improving the accuracy and reliability of liquid level detection.

[0044] In step S1, an excitation signal is output to drive the ultrasonic probe located on the outside of the metal wall to emit ultrasonic waves into the container. The ultrasonic waves penetrate the metal wall and propagate in the liquid medium inside the container.

[0045] During testing, the control unit (such as a microcontroller or DSP chip) first outputs an excitation signal. This excitation signal is processed by the drive circuit and applied to the ultrasonic probe, driving the ultrasonic probe to emit ultrasonic waves into the container. The ultrasonic waves first penetrate the bottom of the stainless steel kettle and enter the water inside. They continue to propagate upwards in the water until they encounter the water surface (i.e., the interface between water and air) and are reflected. The reflected echo returns along the original path to the ultrasonic probe, which converts the echo into an echo electrical signal.

[0046] In step S2, the echo electrical signal received by the ultrasonic probe is acquired, and the echo electrical signal is processed to obtain a level signal characterizing the echo intensity.

[0047] After acquiring the echo electrical signal, the control unit processes it to obtain a level signal characterizing the echo intensity. This level signal is then sampled using analog-to-digital conversion to obtain the corresponding amplitude data. In actual testing, the ultrasonic probe may receive clutter signals in addition to those reflected from the liquid surface, such as reflections from the inner wall of the pot bottom and scattering from impurities in the water. These clutter signals typically have weak amplitudes, while the liquid surface echo has a strong amplitude.

[0048] In step S4, the amplitude data is compared with a preset threshold, and a valid echo is determined based on the comparison result. The control unit compares the sampled amplitude data with the preset threshold. When the amplitude data exceeds the preset threshold, it is determined that a valid echo has been received, which is the ultrasonic echo returned after reflection from the liquid surface. Conversely, if the amplitude data does not exceed the preset threshold, it is determined that the received signal is noise or clutter, and it is not used.

[0049] In step S5, after the control unit determines that a valid echo has been received, it records the liquid level height information based on the time difference between the emitted ultrasonic wave and the received valid echo, and the propagation speed of the ultrasonic wave in the liquid medium.

[0050] The time difference between the start time of emitting the ultrasonic wave and the start time of receiving the effective echo, combined with the propagation speed of the ultrasonic wave in the liquid medium, can be used to calculate the distance the ultrasonic wave travels in the liquid. Half of this distance is the height of the liquid surface relative to the bottom of the pot, thus obtaining the liquid level information.

[0051] In one optional implementation, processing the echo electrical signal to obtain a level signal characterizing the echo intensity includes: The echo signal is amplified, and the amplified signal is rectified and filtered to output a DC level signal that characterizes the echo intensity. The amplification factor for amplifying the echo electrical signal is 50 to 5000 times.

[0052] Specifically, the echo electrical signal received by the ultrasonic probe is usually a weak AC signal with an amplitude in the millivolt or even microvolt range, making it difficult to directly use for subsequent analog-to-digital conversion and threshold comparison. Therefore, this application first uses an amplifier circuit to amplify the echo electrical signal. The amplification factor can be set between 50 and 5000 times, and the specific factor can be adjusted according to factors such as container wall thickness, liquid depth, and the sensitivity of the ultrasonic probe.

[0053] After amplification, the signal remains a high-frequency AC signal. To facilitate subsequent analog-to-digital conversion sampling and amplitude determination, this application further rectifies the amplified signal, converting the high-frequency AC signal into a unidirectional pulsating signal. This unidirectional pulsating signal is then smoothed into a DC level signal through filtering. The voltage amplitude of this DC level signal directly reflects the intensity of the echo signal; the stronger the echo reflected from the liquid surface, the higher the corresponding DC level amplitude. Therefore, the control unit can obtain stable and reliable amplitude data by performing analog-to-digital conversion sampling on this DC level signal, which can then be compared with a preset threshold.

[0054] This implementation converts weak echo AC signals into easily sampled DC level signals through a three-stage signal processing link of amplification, rectification, and filtering, significantly improving the detectability and sampling stability of the echo signals. At the same time, by limiting the amplification factor to the range of 50 to 5000 times, it ensures sufficient amplification of weak signals while avoiding excessive amplification that introduces noise, thus ensuring reasonable gain allocation in the signal conditioning link and improving the signal-to-noise ratio and detection accuracy of the detection system.

[0055] In one alternative implementation, the effective echo is the echo of the ultrasonic wave that returns to the ultrasonic probe after being reflected by the liquid surface inside the container. The time difference is the duration between the start time of transmitting the ultrasonic wave and the start time of receiving the first valid echo.

[0056] Effective echo refers to the echo that returns to the ultrasonic probe after being reflected from the liquid surface inside the container. It is defined as effective echo because, in actual testing, the ultrasonic probe receives multiple reflected signals over a period of time after emitting the ultrasound. These reflected signals may originate from different reflection interfaces. For example, when the ultrasound penetrates the bottom of the container, it will generate some interface reflection at the inner wall. When the ultrasound propagates in the liquid inside the container, it will also generate scattered signals when it encounters air bubbles or suspended matter in the water. These are all interference signals not caused by liquid surface reflection.

[0057] To accurately identify liquid surface reflected echoes from these mixed signals, this application defines effective echoes as those that return along the original path after reflection from the liquid surface, and uses a preset threshold for discrimination. The intensity of liquid surface reflected echoes is significantly higher than other interface reflection or scattering signals, thus enabling accurate identification. Furthermore, the time difference is defined as the duration between the start time of ultrasonic wave transmission and the start time of receiving the first effective echo. Since ultrasonic waves first encounter reflection from the inner wall of the pot bottom (shortest distance, earliest time), then may encounter scattering from impurities in the water, and finally encounter reflection from the liquid surface (farthest distance, latest time), this application uses the first effective echo (i.e., the first echo with an amplitude exceeding the preset threshold) as the liquid surface echo, ensuring that the calculated time difference accurately reflects the actual propagation time of the ultrasonic wave in the water.

[0058] This implementation defines the effective echo as the liquid surface reflection echo and the time difference as the duration between the start of the transmission and the start of the first effective echo. This provides an accurate time reference for subsequent liquid level calculations, avoids calculation deviations caused by using incorrect echo signals, and ensures the accuracy and consistency of the liquid level detection results.

[0059] In one alternative implementation, it further includes: Obtain the temperature of the medium inside the container; The propagation speed of ultrasound in the liquid medium is compensated and corrected based on the medium temperature, and the liquid level height information is calculated using the corrected sound speed.

[0060] In practical applications, the propagation speed of ultrasound in liquid media is not a constant value, but changes with the liquid temperature. Taking water as an example, the propagation speed of ultrasound in water is about 1500 m / s at room temperature (25℃). As the water temperature increases, the speed of sound will increase accordingly (about 1540 m / s at 100℃). In a wide temperature range from room temperature to boiling, the change in speed of sound can reach tens of meters per second. If the effect of temperature is ignored, it will lead to a significant deviation in the liquid level detection results.

[0061] To address this, this application incorporates a temperature sensor within the container. This sensor can be a negative temperature coefficient thermistor or thermocouple, installed at the bottom or side wall of the container and in contact with the liquid, to detect the temperature of the medium inside the container in real time. After acquiring this medium temperature, the control unit corrects the propagation speed of ultrasound in the liquid medium in real time according to a preset sound velocity-temperature compensation curve or formula, obtaining a corrected sound velocity that matches the actual water temperature. This corrected sound velocity is then used to calculate the liquid level information.

[0062] Specifically, the compensation formula can be expressed as v = v0 + k·(T - T0), where v0 is the speed of sound at the reference temperature T0, k is the temperature compensation coefficient, and T is the current water temperature. For example, with a reference temperature of 25℃, v0 is taken as 1500 m / s, and k is taken as 2.5 m / (s·℃). When the water temperature is 100℃, the corrected speed of sound is approximately 1500 + 2.5 × (100 - 25) = 1687.5 m / s. The control unit uses this corrected speed of sound to calculate the liquid level height, thereby eliminating the influence of water temperature changes on the detection accuracy.

[0063] This implementation eliminates the influence of water temperature changes on the propagation speed of ultrasonic waves by introducing a temperature sensor to detect the medium temperature in real time and dynamically compensate for the sound velocity. This allows the liquid level detection to maintain high accuracy across the entire temperature range from cold water to boiling, making it particularly suitable for household appliances such as kettles that operate in a wide temperature range. The temperature compensation is based on real-time correction according to physical principles rather than simple table lookup, and features good continuity and high accuracy.

[0064] In one optional embodiment, the excitation signal is boosted to a preset driving voltage via a driving circuit to drive the ultrasonic probe. The preset driving voltage range is 10V to 200V, and the frequency range of the ultrasonic waves generated by the ultrasonic probe is 0.1MHz to 10MHz.

[0065] Because ultrasonic probes require high-voltage pulse excitation to generate sufficiently strong ultrasonic waves, while the signals directly output by the control unit (such as a microcontroller) are typically 3.3V or 5V logic level signals, they cannot directly drive the ultrasonic probe to generate ultrasonic waves capable of penetrating metal walls. Therefore, this application sets up a driving circuit (specifically a boost circuit) between the control unit and the ultrasonic probe. The excitation signal output by the control unit is boosted to a preset driving voltage by this driving circuit before being applied to the ultrasonic probe.

[0066] In this embodiment, the preset driving voltage range can be from 10V to 200V. The higher the driving voltage, the stronger the ultrasonic energy emitted by the ultrasonic probe, and the stronger its ability to penetrate the metal wall. Considering the acoustic attenuation characteristics of the thin-walled stainless steel pot bottom (0.3mm to 0.8mm), a driving voltage of around 70V is preferred to meet the penetration requirements. Meanwhile, the frequency range of the ultrasonic waves generated by the ultrasonic probe is from 0.1MHz to 10MHz. The lower the frequency, the greater the penetration depth of the ultrasonic waves in the medium, but the relatively lower the resolution; the higher the frequency, the higher the resolution, but the attenuation also increases accordingly. Based on a comprehensive consideration of the container wall thickness and liquid depth, this application preferably uses a frequency of 1MHz, which ensures both sufficient penetration capability and good detection resolution.

[0067] This embodiment ensures that the ultrasonic probe can generate sufficient energy to penetrate the metal wall by limiting the driving voltage range and the ultrasonic frequency range, while taking into account the balance between detection resolution and signal attenuation, so that the detection method can be adapted to the bottom of containers with different wall thicknesses and materials.

[0068] The steps are repeated at a predetermined cycle to obtain continuous liquid level detection results. The liquid level height information obtained from multiple consecutive detections is filtered and then the final liquid level signal is output. In one alternative embodiment, a control signal is generated based on the liquid level information. The control signal is used to perform at least one control operation among anti-dry-burning protection, quantitative water injection control, water level reminder, or automatic heating stop.

[0069] It is understood that in actual operation, liquid level detection is not completed in a single operation, but is performed continuously at predetermined intervals (e.g., once every 100ms). The control unit repeats the steps of claim 1 in each cycle to obtain a continuous sequence of liquid level detection results.

[0070] Considering that a single detection may be affected by accidental factors (such as transient bubble interference, electrical noise, etc.) and produce outliers, the control unit filters the liquid level height information obtained from multiple consecutive detections. For example, it uses median filtering or mean filtering algorithms to remove obvious outliers and then takes the average value, or it uses moving average filtering to smooth the output results before outputting the final liquid level signal. This processing method can effectively suppress transient interference and improve the stability of detection.

[0071] Based on this, the control unit generates corresponding control signals according to the liquid level information to execute various intelligent control functions. Specifically, when the liquid level is lower than the preset anti-dry-burning threshold, the control unit outputs an anti-dry-burning protection signal, cuts off the heating power supply or issues an alarm to prevent the heating plate from being damaged by dry burning; when the user starts the quantitative water filling function, the control unit automatically stops water filling when it detects that the liquid level has reached the preset quantitative water level; when the liquid level is higher than the preset upper limit threshold, the control unit issues a water level reminder signal to remind the user to stop water filling or drain the water; when the liquid level reaches the preset stop heating threshold (such as when the water boils or when it reaches the full water position), the control unit automatically stops heating.

[0072] In this embodiment, periodic detection and filtering effectively suppress random errors and instantaneous interference in a single detection, significantly improving the stability and smoothness of the detection results. At the same time, by combining the liquid level detection results with the intelligent control of the whole machine, multiple practical functions such as anti-dry burning protection, quantitative water injection, water level reminder, and automatic heating stop are realized, expanding the application value of the liquid level detection solution and improving the intelligence level and safety of the product.

[0073] Please see Figure 2 and Figure 3 In another aspect of this application, an ultrasonic liquid level detection system is also provided, corresponding to the method described above, and applied to a container whose bottom is at least partially composed of a metal wall. Taking an electric kettle as an example, the system includes an ultrasonic probe 1, a drive circuit, a signal conditioning circuit, an analog-to-digital conversion circuit, and a control unit (Microcontroller Unit; MCU).

[0074] Please see Figure 3 Ultrasonic probe Figure 3 The ultrasonic transceiver probe; the drive circuit is... Figure 3 The boost circuit in the circuit is used to boost the excitation pulse output from the control unit to drive the ultrasonic probe to emit ultrasonic waves; the signal conditioning circuit is... Figure 3 The operational amplifier circuit and RC low-pass filter circuit (in conjunction with the rectifier stage) are used to amplify and filter the echo signal received by the probe in sequence, and output a DC level signal representing the echo intensity; the analog-to-digital converter circuit is... Figure 3 The AD sampling (which can be integrated into the control unit) is used to convert the DC level signal into amplitude data.

[0075] The ultrasonic probe 1 of this application is disposed on the outer side of the metal wall. It can be a piezoelectric ceramic ultrasonic sensor with integrated transceiver function, which has both ultrasonic wave transmission and ultrasonic wave reception functions. The ultrasonic probe 1 is used to emit ultrasonic waves into the container under the action of a driving signal, and to receive the ultrasonic wave echo reflected back from the liquid surface, converting the echo into a weak electrical signal.

[0076] The drive circuit is electrically connected to the ultrasonic probe 1. It receives the excitation signal from the control unit, amplifies and boosts the excitation signal, and then outputs it to the ultrasonic probe 1 to drive the ultrasonic probe 1 to emit ultrasonic waves. Specifically, the drive circuit can be implemented using a step-up transformer or a charge pump in conjunction with a MOSFET switch, which can boost the low-voltage logic level signal output by the control unit to a high-voltage pulse of 10V to 200V.

[0077] The signal conditioning circuit is electrically connected to the ultrasonic probe 1. Its function is to preprocess the echo signal output by the ultrasonic probe 1, including amplification, rectification, and filtering. First, the weak echo signal is amplified by a preamplifier by 50 to 5000 times. Then, the high-frequency AC signal is converted into a unidirectional pulsating signal by a rectifier diode. Finally, the high-frequency ripple is filtered out by a low-pass filter, and a stable DC level signal is output. The voltage amplitude of this DC level signal directly represents the echo intensity.

[0078] The analog-to-digital converter (ADC) circuit is connected to the signal conditioning circuit and is used to sample the DC level signal output by the signal conditioning circuit, converting it into digital amplitude data for digital processing by the control unit. The ADC circuit can be implemented using an integrated ADC module within the control unit or a separate external ADC chip.

[0079] The control unit is connected to both the drive circuit and the analog-to-digital converter circuit. Its core is a microcontroller or DSP chip, used to output excitation signals to the drive circuit and receive amplitude data from the analog-to-digital converter circuit. The control unit internally runs a preset detection algorithm that compares the amplitude data with a preset threshold to determine whether a valid echo has been received. When a valid echo is detected, the liquid level height information is calculated based on the time difference between the emitted and received ultrasonic waves and the propagation speed of the ultrasonic wave in the liquid medium.

[0080] In this embodiment, the system and method corresponding to the independent claims have constructed a complete hardware implementation architecture. The functions of each circuit module are clearly defined and work together to fully realize the above-mentioned liquid level detection method. The system adopts a modular design with clear interfaces between each unit, which facilitates integration and layout on the circuit board of the home appliance. The ultrasonic probe 1 adopts a transceiver integrated design, which reduces the number of probes and installation complexity, and lowers the system cost. The signal conditioning circuit adopts a rectification and filtering scheme to convert the high-frequency echo signal into a DC level signal, making the subsequent analog-to-digital conversion and threshold comparison simpler and more reliable.

[0081] In one alternative embodiment, the metal wall of the container is a thin-walled stainless steel bottom 2. The ultrasonic probe 1 is attached to the outside of the thin-walled stainless steel bottom 2 by a high-temperature resistant coupling adhesive. The acoustic impedance of the high-temperature resistant coupling adhesive is between the acoustic impedance of the ultrasonic probe 1 and the acoustic impedance of the thin-walled stainless steel bottom 2, and the thermal resistance of the high-temperature resistant coupling adhesive is configured to prevent the heat of the bottom 2 from being transferred to the ultrasonic probe 1.

[0082] The metal wall at the bottom of the container is specifically a thin-walled stainless steel kettle bottom 2. This thin-walled stainless steel kettle bottom 2 has the advantages of good thermal conductivity, corrosion resistance, and compliance with food hygiene requirements, making it a commonly used bottom material for electric kettles. However, there is a significant difference in acoustic impedance between stainless steel and air. If there is an air gap between the ultrasonic probe 1 and the kettle bottom 2, the ultrasonic waves will undergo severe interface reflection when passing through this gap, resulting in most of the acoustic energy failing to enter the water inside the kettle. Only a very small portion of the energy can penetrate, making effective detection difficult.

[0083] To address the aforementioned issues, this application employs a high-temperature resistant coupling adhesive as the coupling medium, attaching the ultrasonic probe 1 to the outer side of the thin-walled stainless steel kettle bottom 2. The acoustic impedance of this high-temperature resistant coupling adhesive lies between that of the ultrasonic probe 1 and the thin-walled stainless steel kettle bottom 2, achieving a gradual transition in value. This reduces sound wave reflection loss at different medium interfaces, allowing ultrasonic energy to be efficiently transferred from the probe to the kettle bottom 2 and penetrate into the water. Simultaneously, the high-temperature resistant coupling adhesive possesses significant thermal resistance, hindering the transfer of high-temperature heat from the kettle bottom 2 to the ultrasonic probe 1. This prevents performance degradation or damage to the ultrasonic probe 1 due to prolonged contact with the high-temperature kettle bottom 2, thus ensuring the probe's reliability and lifespan under all boiling conditions.

[0084] The embodiments of this application employ thin-walled stainless steel as the material for the pot bottom 2, which balances thermal conductivity and acoustic wave penetration performance. The acoustic impedance matching design of the coupling adhesive significantly improves the transmission efficiency of ultrasonic waves from the probe to the pot bottom 2, solving the problem of acoustic energy attenuation caused by acoustic impedance mismatch. The thermal resistance characteristics of the coupling adhesive effectively isolate the heat conduction of the probe from the high temperature of the pot bottom 2, protecting the reliability of the probe in high-temperature working environments. The coupling adhesive can be cured at room temperature without high-temperature baking, simplifying the production process and making it suitable for large-scale mass production of home appliances.

[0085] In one optional embodiment, the container is an electric kettle, which also includes a heating plate 4 disposed below the thin-walled stainless steel kettle bottom 2. The heating plate 4 has a perforated hole for the ultrasonic probe 1 to pass through, and the ultrasonic probe 1 is installed on the outside of the thin-walled stainless steel kettle bottom 2 through the perforated hole. The system also includes an auxiliary pressing plate 3 and a fixing component. The auxiliary pressing plate 3 is pressed onto the side of the ultrasonic probe 1 away from the bottom of the pot 2. The fixing component fixes the auxiliary pressing plate 3 to the heating plate 4 or the bottom of the pot 2 structure so as to press the ultrasonic probe 1 tightly against the bottom of the pot 2 and expel air during the curing process of the coupling adhesive.

[0086] The bottom of an electric kettle typically includes a thin-walled stainless steel base 2 and a heating plate 4 located below the base 2. The heating plate 4 is a heat-conducting plate made of aluminum or aluminum alloy, with a heating element embedded inside to generate heat and conduct it through the base 2 to the water inside the kettle. In related technologies, the heating plate 4 is usually a complete disc-shaped structure, welded or pressed together with the entire base 2.

[0087] In this application, the heating plate 4 has a perforated hole through which the ultrasonic probe 1 passes. The position of this perforated hole corresponds to the non-heated area of ​​the kettle bottom 2, meaning that this area is not directly heated by the heating tube during normal operation and has a relatively low temperature. After the kettle bottom 2 and the heating plate 4 are welded or assembled, the ultrasonic probe 1 is installed on the outside of the thin-walled stainless steel kettle bottom 2 through the perforated hole, making direct contact with the kettle bottom 2 (with a high-temperature resistant coupling adhesive applied between them), rather than being installed on the surface of the heating plate 4. The advantages of this installation method are: the ultrasonic probe 1 can be as close as possible to the kettle bottom 2, avoiding the extension of the sound propagation path and energy attenuation caused by the thickness of the heating plate 4; at the same time, since the perforated hole is located in the non-heated area, the temperature of the probe's working environment is relatively low, which further facilitates heat dissipation and extends the probe's lifespan.

[0088] In addition, the system of this application also includes an auxiliary pressing plate 3 and a fixing component. The auxiliary pressing plate 3 is pressed onto the side of the ultrasonic probe 1 away from the bottom of the pot 2, and the fixing component (e.g., screws or bolts) fixes the auxiliary pressing plate 3 to the heating plate 4 or the structure of the bottom of the pot 2. During the curing process of the coupling adhesive, the auxiliary pressing plate 3, under the action of the fixing component, continuously presses the ultrasonic probe 1 against the surface of the bottom of the pot 2, ensuring that the thickness of the coupling adhesive layer between the probe and the bottom of the pot 2 is uniform and free of air bubbles. This pressing action can effectively expel the air (including air bubbles trapped in the coupling adhesive) between the ultrasonic probe 1 and the bottom of the pot 2, making the coupling adhesive layer dense and continuous, and ensuring unobstructed sound wave transmission. After the coupling adhesive is completely cured, the auxiliary pressing plate 3 and the fixing component remain in place, providing continuous mechanical protection and preventing the ultrasonic probe 1 from falling off.

[0089] In this embodiment, the hollow structure of the heating plate 4 allows the ultrasonic probe 1 to be directly installed on the outside of the pot bottom 2, shortening the sound propagation path and reducing the loss of sound energy during transmission. The probe is installed in a non-heated area, and the thermal resistance isolation of the coupling adhesive provides double protection to prevent the probe's operating temperature from becoming too high, effectively preventing thermal damage. The auxiliary pressure plate 3 and the fixing component provide stable clamping force during the curing of the coupling adhesive, expelling air gaps and ensuring the quality of acoustic coupling. At the same time, they also have a structural protection function during long-term use, preventing the probe from falling off or shifting due to vibration or accidental collision, ensuring the long-term reliability of the product. The structural design of the auxiliary pressure plate 3 and the fixing component is mature and the assembly process is simple.

[0090] In one optional embodiment, the system provided in this application further includes a temperature sensor connected to the control unit for detecting the temperature of the medium inside the container and feeding back a temperature signal to the control unit; The control unit compensates for and corrects the propagation speed of ultrasound in the liquid medium based on the temperature signal, and uses the corrected sound speed to calculate the liquid level information.

[0091] This application further incorporates a temperature sensor to achieve temperature compensation. This temperature sensor is connected to the control unit and is installed inside the container or in contact with the inner wall of the container. It is used to detect the temperature of the medium inside the container and feeds back the detected temperature signal to the control unit in real time. Taking a kettle as an example, the temperature sensor can be an NTC thermistor, located in a recess on the inner wall of the kettle bottom 2. This allows for accurate water temperature measurement without affecting the flatness of the inner wall of the kettle bottom 2. The output signal of the temperature sensor is a resistance value or a voltage value. The control unit converts this signal into a corresponding temperature value through a voltage divider circuit or a dedicated temperature sensing chip.

[0092] Because ultrasonic waves propagate at different speeds in water at different temperatures, to ensure detection accuracy across the entire temperature range, the control unit uses a preset sound velocity-temperature compensation function based on the temperature signal from the temperature sensor to correct the propagation speed of the ultrasonic waves in the liquid medium in real time. This corrected sound velocity corresponds to the actual water temperature, and the liquid level is then calculated using this corrected sound velocity. Specifically, in the initial stage after startup (when the water temperature is low), the control unit uses the sound velocity at room temperature for calculation. As the heating process progresses and the water temperature gradually rises, the control unit continuously adjusts the sound velocity value based on the real-time temperature detection, always maintaining the sound velocity parameter matching the actual water temperature, thereby ensuring that the liquid level calculation results are accurate and reliable across the entire temperature range.

[0093] Temperature compensation can be implemented using either a lookup table method or a formula calculation method. The lookup table method involves pre-setting a sound velocity-temperature correspondence table in the control unit's memory, allowing the control unit to look up the corresponding sound velocity value based on the current temperature. The formula calculation method involves fitting a relationship (such as a linear or polynomial relationship) between sound velocity and temperature based on experimental data, and the control unit then calculates the sound velocity value at the current temperature in real time.

[0094] In one alternative implementation, the temperature sensor provides an accurate source of temperature data for temperature compensation, enabling the system to dynamically adjust the sound velocity parameter based on the real-time water temperature. This eliminates detection errors caused by temperature changes and ensures high accuracy of liquid level detection throughout the entire boiling process. The installation method and temperature measurement principle of the temperature sensor are mature and reliable, low in cost, and easy to integrate into existing products, thus possessing high industrial application value.

[0095] In summary, this application, through its structural design of placing the ultrasonic probe 1 on the outer side of the container bottom, its ultrasonic wave transmission and reception scheme that penetrates the metal wall, its effective echo judgment method based on amplitude threshold, and its water temperature compensation correction mechanism, constitutes a complete ultrasonic liquid level detection technology solution. It can achieve non-contact, high-precision, and reliable liquid level detection across the entire temperature range without opening holes in the inner wall of the container. At the same time, the assembly structure design of the auxiliary pressing plate 3 and the fixing parts takes into account the feasibility of mass production processes and can be widely used in various household appliances with liquid containers made of metal bottoms.

[0096] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An ultrasonic liquid level detection method, applied to a container, wherein the bottom of the container has at least a partial metal wall, characterized in that, Includes the following steps: An excitation signal is output to drive an ultrasonic probe located on the outside of the metal wall to emit ultrasonic waves into the container. The ultrasonic waves penetrate the metal wall and propagate in the liquid medium inside the container. The echo electrical signal received by the ultrasonic probe is acquired, and the echo electrical signal is processed to obtain a level signal characterizing the echo intensity; The amplitude data is obtained by performing analog-to-digital conversion on the level signal; The amplitude data is compared with a preset threshold, and a valid echo is determined based on the comparison result. When a valid echo is received, the liquid level information is obtained based on the time difference between the transmission of the ultrasonic wave and the reception of the valid echo, and the propagation speed of the ultrasonic wave in the liquid medium.

2. The method according to claim 1, characterized in that, Processing the echo electrical signal to obtain a level signal characterizing the echo intensity includes: The echo signal is amplified, and the amplified signal is rectified and filtered to output a DC level signal characterizing the echo intensity. The amplification factor for amplifying the echo electrical signal is 50 to 5000 times.

3. The method according to claim 1, characterized in that, The effective echo is the echo of the ultrasonic wave returning to the ultrasonic probe after being reflected by the liquid surface in the container. The time difference is the duration between the start time of transmitting the ultrasonic wave and the start time of receiving the first valid echo.

4. The method according to claim 1, characterized in that, Also includes: Obtain the temperature of the medium inside the container; The propagation speed of the ultrasonic wave in the liquid medium is compensated and corrected based on the medium temperature, and the liquid level height information is calculated using the corrected sound speed.

5. The method according to claim 1, characterized in that, The excitation signal is boosted to a preset driving voltage by the driving circuit and then drives the ultrasonic probe. The preset driving voltage ranges from 10V to 200V, and the frequency range of the ultrasonic waves generated by the ultrasonic probe ranges from 0.1MHz to 10MHz.

6. The method according to claim 1, characterized in that, The system repeatedly obtains continuous liquid level detection results at a predetermined cycle, and outputs the final liquid level signal after filtering the liquid level height information obtained from multiple consecutive detections. A control signal is generated based on the liquid level information; The control signal is used to perform at least one of the following control operations: anti-dry burning protection, quantitative water injection control, water level reminder, or automatic heating stop.

7. An ultrasonic liquid level detection system, applied to a container, wherein the bottom of the container is at least partially a metal wall, characterized in that, include: An ultrasonic probe, located on the outside of the metal wall, is used to emit ultrasonic waves into the container and receive the ultrasonic echoes reflected back from the liquid surface, converting the echoes into electrical signals. A driving circuit, electrically connected to the ultrasonic probe, is used to receive excitation signals and drive the ultrasonic probe to emit ultrasonic waves. The signal conditioning circuit, electrically connected to the ultrasonic probe, is used to amplify, rectify, and filter the electrical signal to output a DC level signal characterizing the echo intensity. An analog-to-digital converter circuit, connected to the signal conditioning circuit, is used to sample the level signal and convert it into amplitude data; The control unit, connected to the drive circuit and the analog-to-digital conversion circuit respectively, is used to output the excitation signal, compare the amplitude data with a preset threshold and determine whether a valid echo is received based on the comparison result. When it is determined that a valid echo is received, the liquid level height information is calculated based on the time difference between the emitted ultrasonic wave and the received valid echo and the propagation speed of the ultrasonic wave in the liquid medium.

8. The system according to claim 7, characterized in that, The metal wall of the container is a stainless steel bottom, and the ultrasonic probe is attached to the outside of the thin-walled stainless steel bottom by coupling adhesive; The acoustic impedance of the coupling adhesive is between that of the ultrasonic probe and that of the thin-walled stainless steel pot bottom, and the thermal resistance of the coupling adhesive is configured to impede the transfer of heat from the pot bottom to the ultrasonic probe.

9. The system according to claim 8, characterized in that, The container is an electric kettle, and the electric kettle also includes a heating plate disposed below the bottom of the thin-walled stainless steel kettle; The heating plate has a perforated hole for the ultrasonic probe to pass through, and the ultrasonic probe is installed on the outside of the bottom of the thin-walled stainless steel kettle through the perforated hole; The system also includes an auxiliary pressing plate and a fixing component. The auxiliary pressing plate is pressed onto the side of the ultrasonic probe away from the bottom of the pot, and the fixing component fixes the auxiliary pressing plate to the heating plate or the bottom structure of the pot, so as to press the ultrasonic probe tightly against the bottom of the pot and expel air during the curing process of the coupling adhesive.

10. The system according to claim 7, characterized in that, It also includes a temperature sensor, which is connected to the control unit, for detecting the temperature of the medium inside the container and feeding back a temperature signal to the control unit; The control unit compensates and corrects the propagation speed of the ultrasonic wave in the liquid medium based on the temperature signal, and uses the corrected sound speed to calculate the liquid level information.

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