Oxygen Sensor Nernst Voltage Extraction for Lambda 1 Non-Linearity
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Solution Overview
Problem
Existing sensor elements for measuring oxygen concentration in exhaust gases face non-linearity issues at λ = 1, leading to incorrect recordings due to the dependence of voltage on oxygen concentration, causing disturbances in the control system.
Innovation Solution
A sensor element with an electrochemical pump cell and Nernst cell, where the oxygen concentration is regulated to a constant value using a Nernst voltage signal, and a compensated signal is determined by accounting for additional variables like pump current, to improve measurement accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the voltage at the first electrode is used as a control variable, then the control system can regulate the oxygen concentration, but the measurement becomes highly non-linear and incorrect at λ=1 due to the strong dependence of voltage on oxygen concentration
Solution Approach 1:
The invention extracts the Nernst voltage signal (from the third and fourth electrodes) as a separate measurement indicator from the pump cell voltage signal. By using the Nernst cell's voltage output rather than the pump cell's voltage output as the primary measurement signal, the system separates the control function from the measurement function, thereby avoiding the non-linearity and instability issues that occur when both functions are combined in the pump cell voltage.
2Measurement precision
If a compensated signal is determined by accounting for additional variables like pump current, then measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The invention implements feedback by using the Nernst voltage signal (which reflects the actual oxygen concentration in the cavity) as a controlled variable in the control loop. This feedback mechanism allows the system to continuously monitor and adjust the oxygen concentration based on the actual measurement, thereby improving accuracy while maintaining a manageable level of complexity through the use of standard control loop components.
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 provides precise and dynamic measurement of oxygen concentration by compensating for temperature and pressure effects, optimizing control dynamics and stability within the sensor element.
Implementation Method 1
a first solid electrolyte via which the first electrode is conductively connected to the second electrode via oxygen ions
Implementation Method 2
a second solid electrolyte via which the third electrode is conductively connected to the fourth electrode via oxygen ions
Data Source
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AI summary
The invention relates to a method for determining an oxygen concentration (C O2) and nitrogen oxide concentration (C NOx) in a waste gas (100) by means of a sensor element (10). In addition to a Nernst voltage (U vs), a further variable (p) is detected or identified. A compensated signal (x) is determined from the Nernst voltage signal and from the further variable (p), and used as a controlled variable in a control loop. The current flow (IP i) through the pump cell (36) is output as a measurement variable of the oxygen concentration (C O2) in the waste gas (100).