Gas Sensor Calibration Using Ratio-Based Null Reference
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Solution Overview
Problem
Current gas sensors, particularly chemiresistors, require frequent calibration and access to known test samples for accurate readings, making them inconvenient for home or consumer use.
Innovation Solution
A calibration method that relies on the ratio of sensor readings between a null value phase and a positive value phase, independent of absolute values, allowing for calibration only once with known concentrations, and using these ratios to determine gas concentrations in unknown samples without additional calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas sensors are calibrated at the time of use with known test samples, then measurement precision is improved, but device complexity and ease of operation deteriorate due to requiring frequent calibration and access to known test samples
Solution Approach 1:
The patent performs calibration in advance by exposing the sensor to a known concentration of the target gas and recording the response. This preliminary calibration data is stored and used for subsequent measurements, eliminating the need for frequent recalibration and access to known test samples during actual use.
Solution Approach 2:
The system uses ambient air as a null reference and automatically performs self-calibration by comparing sensor responses to the known ambient concentration. The microcontroller automatically processes the ratio of sensor readings to determine unknown concentrations without requiring manual intervention or external calibration samples.
2Measurement precision
If gas sensors are calibrated frequently, then measurement precision is improved, but loss of time increases due to repeated calibration requirements
Solution Approach 1:
The patent performs calibration in advance by exposing the sensor to a known concentration of the target gas and recording the response. This preliminary calibration data is stored and used for subsequent measurements, eliminating the need for frequent recalibration and access to known test samples during actual use.
3Measurement precision
If gas sensors use absolute value readings, then measurement precision is improved, but device complexity increases due to requiring calibration samples and calibration procedures
Solution Approach 1:
The patent transforms the measurement approach from using absolute sensor readings to using ratios of readings. By taking the ratio of the sensor response to the target gas divided by the response to ambient air, the system eliminates the need for absolute calibration while maintaining measurement accuracy through the relative comparison.
Solution Approach 2:
The patent introduces ambient air as an intermediary reference substance with a known null or near-null concentration of the target gas. This intermediary serves as a baseline for comparison, allowing the system to calculate unknown concentrations through ratio calculations without requiring direct calibration against known standards.
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
Enables reliable and sensitive measurement of low gas concentrations without the need for frequent recalibration, suitable for various gases and applications, including breath analysis, with improved convenience and practicality for home and consumer use.
Implementation Method 1
Semiconductor sensors, and metal-oxide-semiconductor sensors (MOS sensors), detect gases by a chemical reaction that takes place when the gas comes in direct contact with the sensor
Implementation Method 2
chemiresistor, which relies on variance in resistance of an electrode (often exponential variance) when a designated gas or gases react with molecules embedded in the electrode surface
Implementation Method 3
one relies on the fact that the resulting response is unique because the ratio of readings by the gas sensor between a phase with or near a null value for the gas being detected, and a phase with a positive value for the gas being detected (i.e., where the measured gas has a concentration above the null value) is independent of absolute value of the positive value
Data Source
AI summary
The invention relates to simplifying calibration of gas sensors, including gas sensors which are portable and for home use, consumer use or medical use including breath gas sensors, where the calibration against samples of a measured gas having a concentration above the null value, is only performed once to establish a set of calibration ratios of measured known gas concentration readings over null sample readings. Thereafter, in use, the ratio of unknown gas concentration in a test sample to a null value (preferably ambient air) is determined without recalibration, and that ratio is compared with the set of calibration ratios to determine the unknown gas concentration by interpolation or extrapolation.