Probe Reference Cell Impedance Self-Diagnosis via Pump Current Control
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Solution Overview
Problem
Probes used to detect gas concentrations in gas mixtures, such as those in vehicle exhaust, face challenges in maintaining reliable and precise operation due to impedance issues in reference cells, which can lead to measurement errors and require complex diagnostic procedures that are not feasible in the field.
Innovation Solution
A method for operating a probe with a pumped reference cell involves determining specific voltage characteristic values at different times to diagnose impedance, allowing for self-diagnosis without the need for a lead and avoiding reference air poisoning, enabling detection of defective probes and compensation for impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a pump current is continuously applied to the reference cell to maintain stable operation, then the reference cell stability is improved, but reference air poisoning occurs due to excessive current amplitude
Solution Approach 1:
The pump current is applied periodically in pulses rather than continuously. The control unit switches the pump current on and off in a periodic manner, allowing the reference cell to be pumped only during specific time windows when needed for maintaining stability, while avoiding continuous exposure to high current that causes reference air poisoning.
Solution Approach 2:
The pump current amplitude and duty cycle are dynamically adjusted based on the impedance diagnosis results. The control unit adapts the pumping parameters in real-time, increasing pumping when impedance indicates contamination and reducing or suspending pumping when the reference cell is clean, thereby preventing reference air poisoning while maintaining stability.
2Difficulty of detecting and measuring
If a lead is added to the pump current to diagnose reference cell impedance, then impedance diagnosis capability is improved, but reference air poisoning occurs due to altered current characteristics
Solution Approach 1:
The pump current is segmented into distinct phases: a diagnostic phase where impedance is measured with minimal or zero pump current, and a pumping phase where the pump current is applied to maintain reference cell stability. This segmentation allows impedance diagnosis without the harmful effects of continuous pumping current.
Solution Approach 2:
Impedance diagnosis is performed preliminarily before applying the full pump current. The control unit first measures the impedance of the reference cell to determine its condition, then decides whether pumping is necessary and at what amplitude, thereby avoiding reference air poisoning by only pumping when truly needed.
3Measurement precision
If complex diagnostic procedures are implemented to detect impedance issues, then measurement precision is improved, but device complexity increases making field diagnostics infeasible
Solution Approach 1:
The probe performs self-diagnosis of its own reference cell impedance using its existing components. The control unit utilizes the pump current switching mechanism and voltage measurements already present in the probe design to automatically monitor and diagnose reference cell impedance without requiring external diagnostic equipment or complex additional hardware.
Solution Approach 2:
The pump current switching mechanism serves multiple functions: it maintains reference cell stability through pumping, enables impedance diagnosis by creating measurable voltage responses, and provides a means for contamination detection. This multi-functionality eliminates the need for separate diagnostic hardware, reducing device complexity while maintaining measurement precision.
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 method enables precise and reliable self-diagnosis of probe impedance, allowing for in-field detection of aged or defective probes and maintaining accurate gas concentration measurements by compensating for impedance changes, thus ensuring reliable operation and extending the lifespan of the probe.
Implementation Method 1
a diagnosis characteristic is determined which is representative of an impedance of the reference cell
Data Source
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AI summary
The invention relates to a method for operating a probe having a pumped reference cell. A first time (T1) is determined, at which a pulse-width-modulated pump current applied to the reference cell is switched on. In accordance with the first time (T1), at least one first voltage characteristic value (Vref1) is determined within a specified first time frame (F1), the at least one first voltage characteristic value being representative of a voltage applied to the reference cell. The pulse-width-modulated pump current applied to the reference cell is switched off at a second time (T2). A third time (T3) is determined, at which a pulse-width-modulated pump current applied to the reference cell is switched off. In accordance with the third time (T3), at least one second voltage characteristic value (Vref2) is determined within a specified second time frame (F2), the at least one second voltage characteristic value being representative of the voltage applied to the reference cell. In accordance with the at least one first voltage characteristic value (Vref1) and the at least one second voltage characteristic value (Vref2), a diagnostic characteristic value (D) is determined, which is representative of an error in the determination of the nitrogen oxide concentration.