Gas Sensor with Au-Pt Cermet Electrode for High NOx Linearity
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Solution Overview
Problem
Conventional gas sensors face challenges in accurately measuring high nitrogen oxide (NOx) concentrations due to deviations from linear relationships, requiring multiple measurement points and model gases, which complicates industrial mass production and reduces measurement efficiency.
Innovation Solution
A limiting current type gas sensor with a sensor element made of oxygen ion conductive solid electrolyte, featuring a cermet inner pump electrode with specific Au—Pt alloy and ZrO2 composition, and a configuration that includes multiple diffusion limiting parts and pump cells to maintain oxygen partial pressure and suppress NOx resolution, ensuring linearity in sensitivity characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional gas sensor uses simple linear relationship for functional relationship, then measurement process is simple, but measurement precision deteriorates in high NOx concentration region
Solution Approach 1:
The patent changes the functional relationship from a simple linear relationship to a piecewise linear relationship with multiple slopes. By dividing the NOx concentration range into different regions (first concentration region with slope a1, second concentration region with slope a2), the measurement system can accurately represent the non-linear characteristics of NOx current across the full concentration range while maintaining ease of calculation through simple linear segments.
2Measurement precision
If multiple measurement points are used to specify functional relationship, then measurement precision improves, but productivity deteriorates due to increased measurement time
Solution Approach 1:
The patent transforms the complex non-linear functional relationship into a piecewise linear form that can be accurately specified using only two measurement points (one in each concentration region). This reduces the measurement time and effort required compared to using multiple measurement points, while still capturing the essential non-linear behavior through the change in slope between regions.
Solution Approach 2:
The patent segments the continuous non-linear functional relationship into two separate linear segments. Each segment is characterized by a different slope (a1 for first concentration region, a2 for second concentration region), allowing the system to maintain high measurement precision while requiring fewer measurement points for calibration.
3Adaptability or versatility
If gas sensor measures high NOx concentration, then measurement range is improved, but measurement precision deteriorates due to deviation from linearity
Solution Approach 1:
The patent introduces a piecewise linear functional relationship with different slopes for different concentration regions. By defining a first linear relationship for lower concentrations (slope a1) and a second linear relationship for higher concentrations (slope a2), the system maintains measurement precision across the entire extended range from low to high NOx concentrations.
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 solution enables accurate NOx concentration measurement up to high levels with improved linearity, reducing the number of measurement points needed and enhancing productivity in industrial applications by maintaining a high straight-line rate, thus ensuring reliable NOx detection.
Implementation Method 1
a sensor element formed of an oxygen ion conductive solid electrolyte
Implementation Method 2
a main pump cell which is an electrochemical pump cell constituted by an inner pump electrode provided to face the first inner space, an external pump electrode provided on a surface of the sensor element, and the solid electrolyte located between the inner pump electrode and the external pump electrode
Implementation Method 3
said measurement electrode functioning as a reduction catalyst for NOx
Implementation Method 4
covered with a porous protection film providing a predetermined diffusion resistance
Data Source
AI summary
A sensor element includes: a first inner space into which a measurement gas is introduced from outside; a second inner space communicated with the first inner space; a main pump cell constituted by an inner pump electrode facing the first inner space, an external pump electrode on a surface of the sensor element, and a solid electrolyte located therebetween; a measurement electrode facing the second inner space and functioning as a reduction catalyst for NOx; and a measurement pump cell constituted by the measurement electrode, the external pump electrode, and a solid electrolyte located therebetween. The inner pump electrode is a cermet made of an Au—Pt alloy containing Au ranging from 0.6 wt % to 1.4 wt % and ZrO2, and has a thickness ranging from 5 μm to 30 μm, a porosity ranging from 5% to 40%, and an area ranging from 5 mm2 to 20 mm2.