Conductivity Sensor Using Real Part Extraction to Reduce Interface Impedance
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Solution Overview
Problem
Existing methods for measuring the conductivity of a liquid using capacitive sensors lack sufficient sensitivity over a wide conductivity range, particularly due to increased impedance at the electrode-liquid interface caused by protective layers.
Innovation Solution
A conductivity measurement method utilizing a conductivity sensor with an insulating layer, detection electrodes, and a protective layer formed of an insulator, where the conductivity is measured by extracting a value from the complex impedance between the electrodes, considering only the real part and ignoring the imaginary part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is formed on the electrode to prevent chemical interaction with the liquid, then the electrode is protected from chemical interaction, but the impedance at the electrode-liquid interface increases
Solution Approach 1:
The protective layer acts as an intermediary between the electrode and the liquid, preventing direct chemical interaction while allowing electrical measurement. The patent applies this by forming an insulating protective layer on the electrode surface that can be processed to control its electrical properties, enabling it to serve as both protection and measurement interface.
Solution Approach 2:
The patent changes the electrical parameters of the protective layer by controlling its formation process (such as plasma treatment or chemical etching) to adjust its insulating properties. This allows the protective layer to maintain its protective function while reducing excessive impedance buildup, enabling accurate conductivity measurements across wide ranges.
2Volume of moving object
If the measurement region is made small to enable portable or compact sensors, then the sensor size is reduced, but the sensitivity to conductivity changes decreases
Solution Approach 1:
The patent compensates for the reduced measurement area by optimizing the electrode geometry in multiple dimensions - using interdigitated finger electrodes that extend in multiple directions, increasing the effective electrode surface area within a compact footprint. This maintains high sensitivity while achieving small sensor size.
Solution Approach 2:
The electrode is segmented into multiple finger-like structures arranged in an interdigitated pattern. This segmentation increases the total electrode surface area and the number of interaction points with the liquid, thereby maintaining high sensitivity even when the overall sensor area is reduced for portability.
3Adaptability or versatility
If the cell constant is changed by adjusting electrode surface area to measure wide conductivity range, then the measurement range is expanded, but the sensor complexity increases
Solution Approach 1:
The patent implements a switching mechanism that can dynamically change the effective electrode surface area by connecting or disconnecting different electrode finger segments. This allows the sensor to adapt its cell constant for measuring different conductivity ranges without requiring multiple separate sensors, thereby expanding measurement range while controlling complexity through a single sensor with variable configuration.
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 method enables precise measurement of liquid conductivity with high sensitivity across a wide conductivity range, ensuring accurate detection even in high conductivity scenarios.
Implementation Method 1
measuring a first complex impedance between the first detection electrode and the second detection electrode at a first frequency with the liquid being in contact with the protective layer to face each of the first detection electrode and the second detection electrode through the protective layer
Implementation Method 2
formation of a capacitance between an electrode and a liquid
Data Source
AI summary
A conductivity measurement method of measuring a conductivity of a liquid includes: a) measuring a first complex impedance between a first detection electrode and a second detection electrode at a first frequency with the liquid being in contact with a protective layer to face each of the first detection electrode and the second detection electrode through the protective layer; b) extracting a first extraction value from the first complex impedance according to a predetermined extraction rule; and c) deciding the conductivity of the liquid based on the first extraction value. In the extraction rule, a real part of a complex impedance is considered, and an imaginary part of the complex impedance is ignored.