Solid Electrolyte Oxygen Sensor with Pump-Measurement Cycle
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Solution Overview
Problem
Existing methods for measuring oxygen partial pressure in gases using solid electrolyte cells face challenges such as moisture interference, construction complexity, and voltage drop issues due to internal resistance, which affect measurement accuracy and robustness, especially at varying temperatures.
Innovation Solution
A method involving a solid electrolyte cell with distinct phases for pumping and measuring, where the oxygen partial pressure in a reference volume is reduced and set to match the measurement gas's pressure, using controlled pump current pulses to maintain a constant measurement voltage, and adjusting internal resistance to minimize temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a solid electrolyte cell is operated as a pump cell to re-set the oxygen partial pressure in the reference volume, then the measurement accuracy is improved, but the device complexity increases due to additional solid electrolyte cells
Solution Approach 1:
The solid electrolyte cell is designed to perform both pumping and measurement functions using the same cell. The cell can be operated in pump mode to adjust oxygen partial pressure in the reference volume and in measurement mode to determine the oxygen content in the measurement gas, eliminating the need for separate cells and reducing device complexity
2Measurement precision
If the solid electrolyte cell is alternately operated as pump and measurement cell to eliminate voltage drop, then the measurement accuracy is improved, but polarisation effects occur which falsify the measurement result
Solution Approach 1:
The measurement method uses periodic action by alternating between pump phase and measurement phase in a cyclic manner. During the pump phase, the oxygen partial pressure in the reference volume is adjusted; during the measurement phase, the voltage is measured. This periodic operation allows the system to account for and compensate polarisation effects by comparing measurements taken at different phases of the cycle
Solution Approach 2:
The method employs feedback by using the measured voltage to determine the oxygen partial pressure quotient and adjusting the pump operation accordingly. The system continuously monitors the measurement voltage and uses this information to control the pumping process, ensuring accurate compensation for polarisation effects and maintaining measurement reliability
3Device complexity
If a diffusion-limiting amperometric method is used for oxygen measurement, then the device structure is simplified, but moisture can penetrate into the sensor via diffusion openings leading to destruction
Solution Approach 1:
The invention extracts or removes the diffusion openings that allow moisture penetration from the sensor structure. By eliminating these openings while maintaining the measurement function through the solid electrolyte cell, the sensor becomes robust against moisture damage while retaining its ability to measure oxygen content accurately
4Measurement precision
If the internal resistance of the solid electrolyte is reduced to minimize voltage drop, then the measurement accuracy is improved, but the internal resistance varies significantly with temperature and lifetime making it difficult to eliminate
Solution Approach 1:
The method uses feedback to continuously monitor the actual voltage drop across the solid electrolyte during operation and compensates for it in the measurement calculation. By measuring the voltage at the electrodes and accounting for the pump current and internal resistance in real-time, the system can accurately determine the oxygen partial pressure quotient despite variations in internal resistance due to temperature and aging
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 enables accurate and robust measurement of oxygen partial pressure with reduced apparatus expenditure, improved moisture resistance, and minimized temperature-dependent errors, ensuring high accuracy and reliability in determining oxygen content.
Implementation Method 1
at least one oxygen-conducting solid electrolyte, for example, made of zirconium dioxide (zirconium IV oxide) between the first electrode and the second electrode
Implementation Method 2
The measurement voltage applied to the electrodes determines, according to the so-called Nernst equation, the oxygen partial pressure quotient between the reference gas and the measurement gas
Data Source
AI summary
Method and apparatus for measurement of the oxygen partial pressure or the oxygen content in a measurement gas in at least one measurement cycle using a solid electrolyte cell having at least one oxygen-conducting solid electrolyte, and having at least one reference electrode as well as at least one measurement electrode, wherein the at least one measurement electrode is in communication with the measurement gas and the at least one reference electrode is in communication with a reference gas or reference volume separated from the measurement gas, wherein a current is imposed via the electrodes on the solid electrolyte cell for pump operation and a measurement voltage (UM) is tapped at the electrodes.