NOx Sensor Correction for Pressure-Induced Accuracy Errors
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Solution Overview
Problem
Conventional NOx detection apparatuses face accuracy issues due to pressure changes in the measured gas, leading to errors in NOx concentration detection across various concentration ranges, as the output variation caused by pressure changes depends on the NOx concentration, and individual sensors have varying diffusion resistance, affecting measurement stability.
Innovation Solution
The NOx detection apparatus incorporates a first and second pumping cell with paired electrodes to adjust oxygen concentration and measure NOx concentration, using concentration variation correction information and pressure information to correct NOx concentration calculations, employing an n-th order function for pressure correction, and setting coefficients based on actual NOx concentration to reduce the influence of pressure changes across the entire concentration range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure correction is performed using fixed correction information, then detection accuracy is improved in a certain NOx concentration range, but detection accuracy deteriorates in other concentration ranges
Solution Approach 1:
The patent applies dynamics by making the correction information variable rather than fixed. The correction information is changed according to the detected NOx concentration, allowing the system to adapt to different concentration ranges. This is implemented by dividing the NOx concentration range into multiple regions and selecting different correction information sets based on which region the current concentration falls into, thereby resolving the contradiction between optimizing for a specific range and maintaining versatility across all ranges.
Solution Approach 2:
The patent applies parameter changes by modifying the correction information parameters based on the NOx concentration level. Different correction coefficients and correction amounts are used for different concentration ranges. This allows the system to optimize detection accuracy for each specific concentration region while maintaining overall versatility across the entire measurement range, directly addressing the contradiction between precision in one range and adaptability across all ranges.
2Stability of the object's composition
If diffusion resistance is increased to stabilize gas flow, then measurement stability is improved, but sensor output variation due to pressure changes increases
Solution Approach 1:
The patent applies feedback by detecting the actual NOx concentration and using this information to correct the sensor output. The system continuously monitors the concentration and adjusts the correction amount accordingly, creating a closed-loop system that compensates for the increased output variation caused by higher diffusion resistance. This feedback mechanism allows the use of higher diffusion resistance for flow stability while maintaining measurement precision through active correction.
Solution Approach 2:
The patent applies preliminary anti-action by pre-calculating and storing correction information for different NOx concentration ranges and pressure conditions. Before actual measurement, the appropriate correction information is selected and prepared based on expected conditions. This preliminary preparation allows the system to counteract the measurement errors caused by pressure variations and diffusion resistance effects, maintaining accuracy despite the trade-off of increased flow stability requirements.
3Reliability
If individual sensor characteristics are accounted for using fixed correction information, then production variation is compensated, but concentration-dependent output variation cannot be corrected
Solution Approach 1:
The patent applies dynamics by transitioning from static, fixed correction information to dynamic, concentration-dependent correction information. Each sensor is provided with multiple sets of correction information corresponding to different NOx concentration ranges, and the appropriate set is selected based on the current concentration level. This dynamic approach maintains reliability by compensating for individual sensor variations while simultaneously improving precision across the entire concentration range.
Solution Approach 2:
The patent applies segmentation by dividing the NOx concentration range into multiple distinct regions and assigning different correction information to each region. This segmentation allows the system to handle different concentration-dependent behaviors separately, ensuring that each region receives optimized correction parameters. This approach resolves the contradiction by maintaining sensor-to-sensor consistency through individualized correction while also addressing concentration-dependent variations through region-specific correction strategies.
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 effectively suppresses the decrease in gas detection accuracy by accurately correcting NOx concentration across the entire range, regardless of pressure changes, and accounts for individual sensor differences, improving measurement precision.
Implementation Method 1
a first pumping cell which has paired first electrodes provided internally and externally of a first measurement chamber and which pumps out oxygen from the to-be-measured gas introduced into the first measurement chamber and pumps oxygen into the first measurement chamber
Implementation Method 2
a second pumping cell which has paired second electrodes provided internally and externally of an NOx measurement chamber communicating with the first measurement chamber and in which a second pumping current corresponding to an NOx concentration in the to-be-measured gas whose oxygen concentration has been adjusted by the first pumping cell flows between the paired second electrodes
Implementation Method 3
the amount of the gas flowing into measurement chambers (the first measurement chamber and the NOx measurement chamber) is limited (controlled) by a predetermined diffusion resistor
Data Source
AI summary
An NOx detection apparatus computes a first NOx concentration NOxpo on the basis of a second pumping current Ip2, and sets correction coefficients a, b (concentration variation correction information) on the basis of the first NOx concentration NOxpo. Therefore, the NOx detection apparatus can set the correction coefficients a, b in accordance with the concentration of NOx actually contained in a to-be-measured gas. Since the NOx detection apparatus uses Equation 3, determined by the correction coefficients a, b, for correction of the first NOx concentration NOxpo, the NOx detection apparatus can correct the first NOx concentration NOxpo in accordance with the state of change of the NOx concentration even when the magnitude of an output variation caused by a pressure change changes depending on the NOx concentration.