Gas Sensor Common Electrode NOx Ammonia Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional multi-gas sensors for NOx and ammonia have limitations in stability and precision due to independent electrode layouts and reference electrode exposure, leading to inadequate correction of NOx concentration measurements when ammonia is present.
Innovation Solution
A gas sensor design featuring a lamination of oxygen-ion conductive solid electrolyte layers with a shared common reference electrode for both NOx and ammonia sensors, utilizing a mixed potential cell and electrochemical pump cells to maintain constant potential differences and control pump currents for precise NOx concentration determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a reference electrode is exposed to the measurement gas to sense ammonia concentration, then ammonia sensing capability is achieved, but the reference potential varies due to oxygen concentration changes, reducing measurement stability
Solution Approach 1:
The sensor element is divided into distinct functional regions: a measurement gas contact region for ammonia sensing and a reference gas contact region for maintaining stable reference potential. The reference electrode is positioned in the reference gas region, physically isolated from the measurement gas, thereby preventing oxygen concentration variations in the measurement gas from affecting the reference potential while maintaining ammonia sensing capability.
2Measurement precision
If independent electrodes and lead wires are provided for each sensor part, then NOx and ammonia can be sensed independently, but the layout constraints reduce design freedom and increase device complexity
Solution Approach 1:
The NOx sensor part and ammonia sensor part share common structural elements including the solid electrolyte layer, reference electrode, and lead wire routing. The inner pump electrode serves as a common electrode for both sensor parts, and the lead wires are routed through common pathways. This merging of common elements reduces the number of independent components and simplifies the overall electrode layout while maintaining independent sensing capabilities for both gases.
3Reliability
If the reference electrode is located inside the sensor element, then the NOx measurement stability is improved, but the ammonia sensor cannot access the measurement gas, reducing ammonia sensing accuracy
Solution Approach 1:
The sensor element utilizes a multi-layered laminated structure with distinct functional regions arranged in different spatial dimensions. The reference electrode is positioned in a reference gas contact region that is spatially separated from the measurement gas contact region where the NH3 sensing electrode is located. This three-dimensional arrangement allows the reference electrode to be shielded from measurement gas variations while the NH3 sensing electrode remains exposed to the measurement gas for accurate ammonia detection.
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 design achieves stable and high-precision NOx concentration measurements even in the presence of ammonia, with a simplified configuration compared to conventional multi-gas sensors, allowing concurrent and precise determination of both NOx and ammonia concentrations.
Implementation Method 1
a NH3 sensing electrode formed on a surface of the sensor element and having catalytic activity inactivated for a NH3 gas
Implementation Method 2
The NH3 sensing electrode, the common reference electrode, and a solid electrolyte between the NH3 sensing electrode and the common reference electrode constitute a mixed potential cell
Implementation Method 3
an outer pump electrode formed on a surface of the sensor element, and has a measurement pump cell that is an electrochemical pump cell constituted by the NOx measurement electrode, the outer pump electrode, and a solid electrolyte between the NOx measurement electrode and the outer pump electrode
Implementation Method 4
a lamination of a plurality of oxygen-ion conductive solid electrolyte layers
Implementation Method 5
a state of controlling a voltage applied across the NOx measurement electrode and the outer pump electrode to maintain a potential difference between the NOx measurement electrode and the common reference electrode constant
Data Source
AI summary
A sensor element includes a NOx sensor part, a NH3 gas sensor part, and a single common electrode shared by the both parts. The former has a pump cell including a measurement electrode facing an internal space, a pump electrode formed on a surface of the element, and a solid electrolyte therebetween. The latter includes a sensing electrode formed on a surface of the element and having catalytic activity inactivated for a NH3 gas. The common electrode is located to be in contact with a reference gas. The NOx concentration is determined based on a potential difference occurring between the sensing electrode and the common electrode, and a current flowing through the pump cell in a state of controlling a voltage applied across the electrodes to maintain a potential difference between the measurement electrode and the common electrode constant.