Conductivity Sensor Multi-Frequency Impedance Tolerance
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Solution Overview
Problem
Existing methods for measuring the conductivity of liquids lack sufficient sensitivity over a wide conductivity range, particularly due to the increase in impedance caused by the protective layer in capacitive sensors.
Innovation Solution
A conductivity measurement method using a conductivity sensor with an insulating layer, detection electrodes, and a protective layer, where complex impedance is measured at two different frequencies, and extraction values are used to determine the conductivity of the liquid within predetermined tolerances.
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 chemical stability of the sensor is improved, but the impedance of the electrode increases, reducing measurement sensitivity
Solution Approach 1:
The patent introduces an insulating layer as an intermediary substance between the electrode and the liquid. This insulating layer prevents direct chemical contact between the electrode and liquid (solving the chemical stability issue) while still allowing electrical field penetration for conductivity measurement (maintaining measurement sensitivity). The insulating layer acts as a mediator that reconciles the conflicting requirements of chemical protection and electrical functionality.
Solution Approach 2:
The patent employs frequency-dependent impedance measurement to overcome the impedance increase caused by the protective layer. By measuring complex impedance at multiple frequencies and extracting appropriate values, the system can compensate for the frequency-dependent effects introduced by the insulating layer and protective layer, thereby maintaining measurement sensitivity across different conductivity ranges.
2Volume of moving object
If the measurement region is kept small for miniaturization, then the device size is reduced, but the measurable conductivity range becomes limited
Solution Approach 1:
The patent transitions from single-frequency to multi-frequency measurement, adding the frequency dimension to the measurement process. By measuring complex impedance at multiple frequencies and using extraction rules to obtain appropriate values, the system extends its measurable conductivity range beyond what would be possible with a single frequency, effectively using frequency as an additional dimension to overcome the limitations of miniaturization.
Solution Approach 2:
The patent changes the measurement parameter from simple resistance to complex impedance, and further to frequency-dependent extraction values. This parameter transformation allows the small sensor to measure a wide conductivity range by analyzing how the impedance varies with frequency, extracting meaningful conductivity information that compensates for the limited physical measurement region.
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 ensures sufficient sensitivity for measuring conductivity over a wide range, allowing for accurate determination of liquid conductivity even under the influence of the protective layer.
Implementation Method 1
formation of a capacitance between an electrode and a liquid
Implementation Method 2
measuring a first complex impedance between the first detection electrode and the second detection electrode at a first frequency
Data Source
AI summary
A conductivity measurement method includes: a) measuring a first complex impedance between a first detection electrode and a second detection electrode at a first frequency with a liquid being in contact with a protective layer to face each of the first and second detection electrodes through the protective layer; b) extracting a first extraction value from the first complex impedance according to an extraction rule; c) determining whether the first extraction value is within a tolerance; d) deciding a conductivity of the liquid based on the first extraction value when it is determined that the first extraction value is within the tolerance in c); and e) deciding the conductivity of the liquid based on a second extraction value extracted according to the extraction rule from a second complex impedance at a second frequency when it is determined that the first extraction value is outside the tolerance in c).