Capacitance Liquid Level Sensing With Switched Electrodes
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Solution Overview
Problem
Existing liquid level detection methods face challenges such as uneven resistance values due to abrasion or dust adhesion, increased manufacturing costs with long cables, and accuracy issues due to parasitic capacitance, especially when detecting electrically insulating liquids.
Innovation Solution
A sensor system with two electrodes that alternate functions as input and drive electrodes, reducing dust adhesion and parasitic capacitance effects, and capable of accurate detection regardless of liquid conductivity, using a ground pattern for contact and shielded wires to maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional liquid level detection methods are used, then detection can be performed, but accuracy deteriorates due to parasitic capacitance and dust adhesion
Solution Approach 1:
The patent implements periodic alternation between drive electrode and input electrode roles for the first and second electrodes. This periodic switching reduces the accumulation of dust adhesion and minimizes parasitic capacitance effects, thereby maintaining accurate liquid level detection over time despite the presence of harmful factors.
2Ease of operation
If long cables are used to connect the sensor, then installation flexibility improves, but manufacturing cost increases
Solution Approach 1:
The patent introduces a shield wire as an intermediary element between the sensor and external circuitry. This shield wire acts as a mediator that allows for longer cable connections while maintaining signal integrity and reducing interference, thus enabling installation flexibility without proportionally increasing manufacturing costs.
3Adaptability or versatility
If the sensor detects electrically insulating liquids, then application range expands, but detection accuracy deteriorates due to parasitic capacitance
Solution Approach 1:
The periodic switching between drive and input electrode roles is particularly effective for electrically insulating liquids. This alternation prevents parasitic capacitance from dominating the measurement signal, enabling accurate detection across a broader range of liquid types including insulating ones.
Solution Approach 2:
The patent changes the operational parameters by alternating the functional roles of electrodes and using shielded connections, which modifies the electrical characteristics of the measurement system. This allows accurate detection of electrically insulating liquids by reducing the influence of parasitic capacitance through parameter optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate and stable liquid level detection across various lengths and types of liquids, including insulating ones, with reduced adhesion and parasitic capacitance interference, ensuring reliable measurements.
Implementation Method 1
a ground pattern on a first surface of the sensor is positioned to contact a liquid in the cavity
Implementation Method 2
A cable coupling the sensor to a touch sensor includes a shield line that is coupled to ground
Implementation Method 3
Capacitance liquid level sensor
Data Source
AI summary
In accordance with at least one embodiment, a method for detecting a liquid level includes providing a container (402) having a cavity, and disposing a sensor (102) in the cavity of the container (402), such that a ground pattern (310) on a first surface of the sensor (102) is positioned to contact a liquid in the cavity. A first electrode (104) and a second electrode (106) are located on a second surface of the sensor (102). The sensor (102) is coupled to a sensor input and a sensor driver. A cable coupling the sensor (102) to a touch sensor (116) comprises a shield line (112, 114) that is coupled to ground.