Non-contact capacitance liquid level sensor

Abstract

The utility model relates to the technical field of liquid level sensing, in particular to a non-contact capacitance liquid level sensor which comprises a cavity outer wall and further comprises a first capacitance plate and a second capacitance plate which are arranged on the cavity outer wall, the first capacitance plate and the second capacitance plate are shortened to form interdigitals, and the interdigitals are arranged in the direction perpendicular to the liquid level change direction. When the liquid level in the cavity rises or falls, the dielectric constant of the liquid is different from that of the air, so that the capacitance value between the interdigital electrodes changes. Liquid level measurement can be achieved by measuring capacitance changes and combining the signal processing module to calculate the corresponding relation between the capacitance and the liquid level. The sensor is mounted on the outer wall of the cavity and does not need to be in direct contact with liquid, so that the problems of pollution, corrosion and mechanical wear of a traditional contact sensor are avoided, and the service life and reliability of the sensor are improved. In addition, the device has the advantages of stable measurement, quick response, high precision and the like.

Description

Technical Field

[0001] This utility model relates to the field of liquid level sensing technology, specifically to a non-contact capacitive liquid level sensor. Background Technology

[0002] Liquid level measurement is an important technology in fields such as industrial production, medical equipment, environmental monitoring, and household appliances. The traditional measurement method is mainly contact liquid level measurement.

[0003] Contact-based liquid level measurement technology typically requires the sensor to be in direct contact with the liquid to sense changes in the liquid level. Common methods include float-type, pressure-type, conductivity-type, and resistance-type sensors. Contact sensors are in prolonged contact with liquids, making them susceptible to corrosive liquids, which can shorten sensor lifespan and even contaminate the measured liquid. This contamination can have serious consequences, especially in the food, pharmaceutical, and chemical industries.

[0004] In particular, existing technologies often rely on temperature changes to measure liquid levels. This is essentially still a contact measurement method because the temperature sensor needs to be placed inside the liquid or in direct contact with it, inferring the liquid level by sensing the temperature difference between the liquid and the air. Since temperature sensors depend on heat conduction, their response time is long, making it impossible to reflect rapid changes in liquid level in real time. Furthermore, changes in temperature gradients are often relatively slow, resulting in low measurement resolution and accuracy, making it difficult to meet the requirements for high-precision measurements. Utility Model Content

[0005] To address the above problems, this utility model provides a non-contact capacitive liquid level sensor, including an outer wall of a chamber, and a first capacitor plate and a second capacitor plate disposed on the outer wall of the chamber. The first capacitor plate and the second capacitor plate form interdigitated fingers, which are arranged in a direction perpendicular to the liquid level change.

[0006] When the liquid level in the chamber rises or falls, the dielectric constant of the liquid differs from that of air, causing a change in the capacitance between the interdigitated electrodes. By measuring this capacitance change and calculating the correlation between capacitance and liquid level using a signal processing module, liquid level measurement can be achieved. Since the sensor is mounted on the outer wall of the chamber and does not need to be in direct contact with the liquid, it avoids the contamination, corrosion, and mechanical wear problems of traditional contact sensors, thus improving the sensor's lifespan and reliability. Furthermore, this invention is unaffected by liquid density, conductivity, and color, providing stable measurement and rapid response. It is particularly suitable for applications involving high-cleanliness environments, corrosive liquids, viscous liquids, or dynamic liquid level changes, and is widely used in chemical, food, pharmaceutical, and industrial automation fields.

[0007] Furthermore, it also includes a circuit board, on which the first and second capacitor plates are placed. This invention integrates the first and second capacitor plates on the circuit board, forming an interdigitated electrode structure on the surface of the circuit board through precision manufacturing processes. The circuit board uses a high-insulation, low-dielectric-loss material, and metal electrodes are manufactured on its surface using etching, screen printing, or sputtering deposition processes, so that the first and second capacitor plates are arranged in an interdigitated pattern and distributed along a direction perpendicular to the liquid level change. The electrodes on the circuit board are connected to a signal processing circuit, which can collect capacitance change data in real time and calculate the liquid level height through embedded algorithms. Because the capacitor plates are integrated on the circuit board, it not only simplifies the sensor structure and improves production consistency but also makes installation more convenient, facilitates large-scale manufacturing, and further improves the stability and accuracy of the measurement.

[0008] Furthermore, the second capacitor plate comprises multiple second sub-capacitor plates, which are disconnected from each other. The second capacitor plate consists of multiple disconnected second sub-capacitor plates, which operate independently, forming multiple interdigitated capacitor units with the first capacitor plate. When the liquid level rises or falls, the second sub-capacitor plates at different heights sense different changes in dielectric constant, thereby measuring the liquid level height. In use, the signal processing module collects the capacitance change of each second sub-capacitor plate separately and calculates the liquid level information comprehensively. This design has the advantage of improving measurement accuracy and resolution because multiple independent measurement units can capture liquid level changes more precisely, while effectively reducing parasitic capacitance interference and improving measurement stability. In addition, the disconnected structure between the sub-capacitor plates enhances anti-interference capabilities, reducing the impact of factors such as temperature drift and electric field noise on the measurement results, enabling the sensor to maintain high-precision measurements in different liquid environments. Especially in liquid sloshing or complex dynamic liquid level measurement scenarios, this segmented detection method can optimize measurement linearity, reduce errors, and make the measurement more stable and reliable.

[0009] Furthermore, the first capacitor plate includes multiple first sub-capacitor plates, the number of which is the same as the number of second sub-capacitor plates. Each first sub-capacitor plate and each second sub-capacitor plate form an interdigitated unit. In use, each interdigitated unit acts as an independent capacitance measurement point, sensing the capacitance change corresponding to the liquid level height. The signal processing module then performs comprehensive calculations on the data from all interdigitated units to obtain more refined liquid level distribution information. Because liquid level changes affect the capacitance values ​​of multiple interdigitated units, the system can fit data from multiple independent measurement points to obtain more accurate liquid level measurement results.

[0010] Furthermore, the distance between adjacent interdigitated units is greater than the interdigital spacing. Due to the larger spacing between interdigitated units, the mutual influence of electric fields between different measurement units is reduced, thereby reducing parasitic capacitance effects and improving the independence and accuracy of measurements.

[0011] Furthermore, it also includes a porous material section, which is a thin layer attached to the inner wall of the chamber. When the liquid is subjected to external disturbances (such as vibration, tilting, or fluid impact), traditional liquid level measurement methods are easily affected by fluctuations, leading to unstable measurement values. This invention, by attaching a porous material section to the inner wall of the chamber, can effectively suppress liquid sloshing. The porous material section enables the liquid level to remain relatively stable within the sensor's measurement area, thereby improving measurement accuracy and repeatability, and avoiding erroneous measurements caused by brief fluctuations.

[0012] Furthermore, the material of the porous material section is a porous foam material.

[0013] Furthermore, the porous material section contains periodically arranged holes.

[0014] Furthermore, the orifice is oriented downwards. When the liquid sloshes or flows, the downward-sloping orifice structure guides the liquid to flow out smoothly, preventing liquid from stagnating inside the orifice and improving measurement stability.

[0015] Furthermore, the holes can be round, square, or hexagonal.

[0016] The beneficial effects of this utility model are:

[0017] (1) In this utility model, the capacitive sensing response is fast and can detect liquid level changes in real time, making it suitable for dynamic liquid level monitoring scenarios.

[0018] (2) The interdigitated electrode structure of this utility model can accurately sense minute capacitance changes and realize high-resolution liquid level measurement.

[0019] (3) The sensor of this utility model is installed on the outer wall of the chamber, which is completely isolated from the liquid and is not corroded by the liquid. It is particularly suitable for fields with high cleanliness requirements such as food, medicine and chemical industry.

[0020] (4) This invention is not affected by liquid density, conductivity, color or viscosity, and can be used in various liquid media, including corrosive liquids, high-purity liquids and viscous liquids.

[0021] (5) This utility model has no mechanical wear, is stable and reliable for long-term use, does not require frequent cleaning and calibration, and reduces maintenance costs.

[0022] Considering the above effects, this utility model has good application prospects in the field of liquid level measurement. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a non-contact capacitive liquid level sensor.

[0024] Figure 2 This is a schematic diagram of another type of non-contact capacitive liquid level sensor.

[0025] Figure 3 This is a schematic diagram of another type of non-contact capacitive liquid level sensor.

[0026] In the figure: 1. External wall of the chamber; 2. First capacitor plate; 3. Second capacitor plate; 21. First sub-capacitor plate; 31. Second sub-capacitor plate. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments.

[0028] Example 1

[0029] This invention provides a non-contact capacitive liquid level sensor, such as... Figure 1 As shown, the system includes an outer wall 1 of the chamber, a first capacitor plate 2, and a second capacitor plate 3. Liquid is contained within the chamber, with the liquid level vertical. The first capacitor plate 2 and the second capacitor plate 3 form an interdigitated structure and are arranged perpendicular to the direction of liquid level change to improve the resolution and accuracy of liquid level detection.

[0030] In this embodiment, both the first capacitor plate 2 and the second capacitor plate 3 have the same length of 100mm, width of 10mm, and thickness of 0.1mm. The interdigitated portion consists of multiple parallel electrodes, each with a width of 2mm and a spacing of 1mm between the interdigitated electrodes to ensure good capacitive sensing characteristics.

[0031] The outer wall 1 of the chamber is made of a low dielectric constant material with a thickness of 3 mm to ensure that the capacitive signal of the sensor can effectively penetrate the chamber wall without being affected by the material's shielding effect. The first capacitor plate 2 and the second capacitor plate 3 are made of 35-micron thick copper foil, and an interdigitated structure is formed through an etching process. The circuit board is made of fiberglass board with a thickness of 1.6 mm and is covered with a solder resist layer to prevent oxidation and extend its service life.

[0032] This sensor is based on the interdigital capacitance measurement principle. The first capacitor plate 2 and the second capacitor plate 3 form an interdigital structure. When the liquid level rises or falls, the distribution of liquid within the interdigital region changes, thereby altering the capacitance value between the plates. Specifically, when the liquid level rises, the interdigital region is filled with more liquid. Since the dielectric constant of liquid (approximately 80) is much greater than that of air (approximately 1), the capacitance value increases accordingly. When the liquid level falls, the proportion of air in the interdigital region increases, and the capacitance value decreases. By detecting the capacitance change and combining it with calibration data from the signal processing module, the liquid level height can be accurately calculated. In this embodiment, the sensor is driven by a 1MHz high-frequency signal.

[0033] During installation, the circuit board is fixed to the outer side of the outer wall 1 of the chamber using high-strength double-sided adhesive or mechanical screws, with the capacitor plates in close contact with the chamber wall to optimize signal sensing. The circuit board integrates a signal processing module and is connected to the control system via shielded wires to prevent external electromagnetic interference from affecting measurement accuracy.

[0034] Example 2

[0035] This embodiment optimizes the structural design, measurement parameters, and signal processing method of the non-contact capacitive level sensor for the washing machine liquid level measurement environment, thereby improving measurement accuracy, anti-foam interference capability, and dynamic response performance. The first capacitor plate 2 and the second capacitor plate 3 are both set to the same length and adopt an asymmetrical interdigitated structure, with each interdigitated finger being 1.5mm wide and spaced 0.5mm apart. Furthermore, the first capacitor plate 2 and the second capacitor plate 3 are integrated onto a flexible circuit board and fitted to the outer wall of the washing machine drum, avoiding direct contact with water flow impact and improving resistance to water flow disturbance. Simultaneously, to reduce foam interference, this embodiment employs dual-frequency measurement technology, acquiring signals within the 100kHz-500kHz range. Combined with a dynamic threshold algorithm, it can distinguish the difference in dielectric constant between liquid and foam, ensuring accurate and reliable water level measurement. To further improve the washing machine's water-saving performance, this embodiment optimizes the fast response mode; when the drain valve is detected to be open, the sampling interval is shortened from 100ms to 50ms to ensure real-time updates of the liquid level data. The sensor in this embodiment features high precision, anti-interference, low power consumption, and fast response, and can be widely used in fields such as smart washing machines, energy-saving home appliances, and efficient water resource management.

[0036] Example 3

[0037] Based on Embodiment 1, the second capacitor plate 3 is composed of multiple non-interconnected second sub-capacitor plates 31. Figure 2 Only two second capacitor plates 31 are shown in the figure. Each second capacitor plate 31 forms an independent interdigitated unit with the first capacitor plate 2 to improve the measurement resolution, anti-interference ability and stability.

[0038] Unlike Embodiment 1, in this embodiment, the second capacitor plate 3 is divided into multiple independent second sub-capacitor plates 31. Each second sub-capacitor plate 31 is disconnected from each other, but is still arranged in a direction perpendicular to the liquid level change to form multiple independent measurement areas.

[0039] The operation of this embodiment is similar to that of Embodiment 1. However, since the second capacitor plate 3 is divided into multiple independent second sub-capacitor plates 31, each second sub-capacitor plate 31 forms a separate measurement unit. The system can independently collect the capacitance values ​​of multiple measurement units, thereby obtaining more detailed liquid level change information. As the liquid level rises, the second sub-capacitor plates 31 at different heights are gradually covered by liquid, and their corresponding capacitance values ​​change.

[0040] Because each of the second capacitor plates 31 is independent, the system can analyze the capacitance value at each measurement point separately, thereby improving measurement resolution and avoiding the impact of outliers in a single area on the overall measurement. Since each second capacitor plate 31 independently measures the liquid level at different heights, the measurement accuracy changes from overall measurement to multi-point segmented measurement, resulting in higher resolution. Furthermore, the disconnection between the second capacitor plates 31 effectively reduces parasitic capacitance and noise interference, improving measurement stability.

[0041] Example 4

[0042] Based on Embodiment 3, the first capacitor plate 2 is composed of multiple first sub-capacitor plates 21. Figure 3 Only two first capacitor plates 21 are shown in the diagram, and they correspond one-to-one with multiple second capacitor plates 31. Each pair of corresponding first capacitor plates 21 and second capacitor plates 31 forms an interdigitated unit. In addition, the distance between adjacent interdigitated units is 3mm, which is greater than the interdigital spacing within the interdigitated units, in order to reduce inter-unit interference and improve measurement accuracy and stability.

[0043] Each first subcapacitive plate 21 and its corresponding second subcapacitive plate 31 constitute an independent interdigital capacitance measurement unit, capable of sensing liquid level changes at corresponding heights. When the liquid level rises, the lower-positioned interdigital units are covered by liquid first, and their capacitance increases initially. As the liquid level continues to rise, it gradually affects the higher-positioned interdigital units, causing their capacitance values ​​to gradually increase. When the liquid level falls, the reverse process occurs, with the capacitance values ​​of each interdigital unit decreasing sequentially. Due to the large spacing between adjacent interdigital units, electric field interference between measurement units is effectively reduced, making the capacitance changes of each unit more independent and improving the accuracy of liquid level measurement.

[0044] Example 5

[0045] Based on the above embodiments, a porous material is attached to the inner wall of the chamber to reduce liquid sloshing, foam interference, and localized stagnant liquid problems. This porous material is a thin-layered porous foam material, 3mm-5mm thick, with periodically arranged holes inside, all of which are tilted downwards at an angle of approximately 30°. o -45 o This design guides the liquid down the wall, improving measurement stability and reducing the impact of water flow fluctuations on capacitive sensing. The orifice shape can be selected from circular, square, or hexagonal depending on the liquid characteristics. Circular orifices are suitable for low-viscosity liquids (such as water and alcohol), square orifices for medium-viscosity liquids (such as dairy products and oils), while hexagonal orifices help to evenly distribute the fluid, making them suitable for environments containing air bubbles or unevenly mixed liquids. When the liquid level rises or falls, this structure buffers the water flow and reduces instantaneous fluctuations, making the liquid level data measured by the capacitive sensor more stable and reliable. Simultaneously, the downward-sloping orifice accelerates liquid discharge, preventing liquid stagnation and improving the real-time performance and consistency of the liquid level measurement. Furthermore, the orifice material effectively disrupts bubble stability, accelerating bubble rise and dissipation, reducing foam interference with capacitive measurements, and making the measurement more accurate. This solution is applicable to scenarios such as intelligent water level detection in washing machines, liquid level control in chemical reactions, food processing, and medical infusion monitoring, ensuring that liquid level measurement maintains high accuracy, stability, and reliability even in complex fluid environments and under dynamic liquid level changes.

[0046] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A non-contact capacitive liquid level sensor, comprising an outer wall of a chamber, characterized in that: It also includes a first capacitor plate and a second capacitor plate disposed on the outer wall of the chamber, the first capacitor plate and the second capacitor plate forming interdigitated fingers, the interdigitated fingers being arranged in a direction perpendicular to the liquid level change.

2. The non-contact capacitive liquid level sensor as described in claim 1, characterized in that: It also includes a circuit board, on which the first capacitor plate and the second capacitor plate are placed.

3. The non-contact capacitive liquid level sensor as described in claim 1, characterized in that: The second capacitor plate includes multiple second sub-capacitor plates, which are disconnected from each other.

4. The non-contact capacitive liquid level sensor as described in claim 3, characterized in that: The first capacitor plate includes multiple first sub-capacitor plates, the number of which is the same as the number of second sub-capacitor plates, and one first sub-capacitor plate and one second sub-capacitor plate form an interdigitated unit.

5. The non-contact capacitive liquid level sensor as described in claim 4, characterized in that: The distance between adjacent interdigital units is greater than the interdigital spacing.

6. The non-contact capacitive liquid level sensor according to any one of claims 1-5, characterized in that: It also includes a porous material section, which is a thin layer and is attached to the inner wall of the cavity.

7. The non-contact capacitive liquid level sensor as described in claim 6, characterized in that: The material of the porous material section is a porous foam material.

8. The non-contact capacitive liquid level sensor as described in claim 6, characterized in that: The porous material section has periodically arranged holes.

9. The non-contact capacitive liquid level sensor as described in claim 8, characterized in that: The hole is oriented downwards.

10. The non-contact capacitive liquid level sensor as described in claim 9, characterized in that: The holes can be circular, square, or hexagonal.

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