Non-contact Liquid Sensing via Multi-frequency Impedance Analysis
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Solution Overview
Problem
Conventional non-contact liquid sensing methods fail to accurately measure liquid properties in dynamic environments due to grounding impacts, film, and foam on container walls, and are sensitive to manufacturing tolerances and temperature dependencies, leading to false readings and inability to distinguish liquid volume from film and foam.
Innovation Solution
A multi-port network-based non-contact liquid sensing method combining self-capacitance and mutual-capacitance sensing at multiple frequency ranges, which measures absolute liquid electrical properties by determining independent impedances of the container, liquid, and ambient ground, thereby isolating liquid properties from container and environmental influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional non-contact liquid sensing methods are used, then the sensing can be performed without contact, but the measurement accuracy deteriorates due to grounding impacts, film, and foam on container walls
Solution Approach 1:
The patent segments the sensing system into multiple independent measurement channels operating at different frequencies. By dividing the measurement into multiple frequency components (e.g., low frequency for liquid conductivity, high frequency for permittivity), the system can distinguish between liquid properties and container wall effects, thereby maintaining non-contact operation while improving measurement accuracy
Solution Approach 2:
The patent changes the operating frequency parameter to differentiate between liquid properties and container influences. By performing measurements at multiple frequency ranges and analyzing the frequency-dependent response, the system can separate the effects of liquid conductivity, liquid permittivity, and container wall capacitance, thus improving measurement precision while maintaining non-contact capability
2Device complexity
If conventional sensing methods are used, then the system is simpler, but the reliability deteriorates due to sensitivity to manufacturing tolerances and temperature dependencies
Solution Approach 1:
The patent implements feedback by continuously monitoring measurements at multiple frequencies and using the frequency-dependent response to compensate for environmental variations. The system uses the ratio or difference between measurements at different frequencies to cancel out temperature-dependent effects and manufacturing tolerance variations, thereby improving reliability without significantly increasing device complexity
Solution Approach 2:
The patent introduces dynamic measurement by performing sensing operations at multiple frequency ranges rather than a single static frequency. This dynamic approach allows the system to adapt to varying conditions by selecting appropriate frequency combinations based on the measured response, improving reliability while maintaining manageable system complexity
3Productivity
If conventional methods are used, then the measurement process is faster, but the measurement precision deteriorates due to inability to distinguish liquid volume from film and foam
Solution Approach 1:
The patent performs partial measurements at different frequency ranges to extract specific information. By using low frequency measurements primarily for conductivity (which is less affected by foam and film) and high frequency measurements for permittivity (which provides volume information), the system achieves accurate liquid volume detection without requiring excessive measurement time, thus maintaining productivity while improving precision
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
This approach allows for accurate measurement of liquid properties, including conductivity and permittivity, while minimizing the impact of container walls and environmental conditions, providing stable readings even with film and foam present, and improving accuracy by distinguishing liquid volume from film and foam.
Implementation Method 1
measuring a first current through the container and liquid at a first frequency and measuring a second current through the container at a second frequency that is lower than the first frequency
Implementation Method 2
measuring a first current indicative of a self-capacitance of a first electrode of a first set of electrodes, the first electrode being located at a first point on an exterior surface of a container that holds a liquid
Implementation Method 3
determining an electrical property of the liquid using the independent impedances of the liquid
Data Source
AI summary
Technology directed to non-contact liquid sensing is described. One processing device includes a multi-port network, a capacitance measurement circuit, and a digital processing circuit. Processing device measures a first set and a second set of currents associated with a first electrode and a second electrode coupled to an exterior surface of a container holding liquid. Processing device determines independent impedances of the container, the liquid, and the liquid and container using the first set of currents and the second set of currents. Processing device determines an electrical property of the liquid using the independent impedances of the liquid.