Gas Sensor Amplifier Circuit Segmentation for Dual Signal Detection
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Solution Overview
Problem
Existing gas concentration detection apparatuses face challenges in accurately measuring both gas concentrations and sensor element impedance due to large differences in signal magnitudes, leading to reduced accuracy in air/fuel ratio detection.
Innovation Solution
A gas concentration detection apparatus with separate amplifier circuits for DC and AC signal components, allowing for appropriate amplification of each signal type, is employed. This apparatus includes a sensor element with a solid electrolyte layer and a current measurement resistor, where an AC voltage source and a reference voltage source apply voltages to the sensor element, generating DC and AC current components that are processed through distinct detection signal output circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single amplifier circuit is used to detect both DC current component (gas concentration) and AC current component (sensor impedance), then the device complexity is reduced, but the measurement precision of gas concentration deteriorates due to large differences in signal magnitudes
Solution Approach 1:
The patent divides the signal processing path into two separate amplifier circuits: a first amplifier circuit for amplifying the DC current component (gas concentration signal) and a second amplifier circuit for amplifying the AC current component (sensor impedance signal). This segmentation allows each amplifier to be optimized for its specific signal type, preventing the DC signal from being overwhelmed by the larger AC signal and thereby maintaining high measurement precision for gas concentration detection.
2Measurement precision
If the amplification gain is set to detect small DC current component, then the gas concentration measurement precision is improved, but the AC current component exceeds the amplification range causing loss of information
Solution Approach 1:
The patent implements separate amplifier circuits with different gain settings: the first amplifier circuit uses a gain optimized for detecting small DC current components (gas concentration), while the second amplifier circuit uses a gain suitable for detecting larger AC current components (sensor impedance). This segmentation prevents signal saturation and information loss by ensuring each amplifier operates within its optimal dynamic range for its specific signal type.
3Measurement precision
If additional amplifier stages are added to detect both signal components accurately, then the measurement precision of both gas concentration and sensor impedance is improved, but the device complexity increases
Solution Approach 1:
The patent employs a segmented amplifier architecture where the first amplifier circuit is dedicated to DC signal amplification and the second amplifier circuit is dedicated to AC signal amplification. This segmentation eliminates the need for complex multi-stage amplifiers with variable gain settings or frequency selective circuits, achieving accurate dual signal detection with a relatively simple and elegant circuit structure.
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 high-accuracy detection of both gas concentrations and sensor element impedance, avoiding the need for additional amplifier stages and reducing errors in air/fuel ratio measurement.
Implementation Method 1
a sensor element (10) which incorporates a solid electrolyte layer (11) and is responsive to an applied voltage for passing a sensor current
Implementation Method 2
The impedance of the sensor element (i.e., at any specific value of AC frequency) varies in accordance with the activation status of the sensor element
Implementation Method 3
a current which flows through the series-connected combination varies in level in accordance with the concentration of a specific constituent gas
Data Source
AI summary
A gas concentration detection apparatus includes a series-connected combination of a sensor element and a resistor, with an AC voltage being applied to one of the outer terminals of that combination and with the other outer terminal being held at a fixed potential. A DC voltage signal at a level determined by an oxygen concentration that is detected by the sensor element, and an AC voltage signal at an amplitude determined by sensor element impedance and hence by the sensor element activation status, are extracted from the series-connected combination by respectively separate circuits which apply separately determined amplification factors.