Calibrating Non-Selective Chemical Sensors Using Reference Signals
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Solution Overview
Problem
Non-selective chemical sensors, such as semiconductor sensors, require frequent calibration due to drift in their response over time, especially due to the adsorption of volatile organic compounds (VOCs), which affects the accuracy of VOC concentration measurements in air quality monitoring, necessitating regular recalibration and potential false readings if not properly maintained.
Innovation Solution
A method and system for calibrating non-selective chemical sensors using a reference sensor that measures correlated signals, allowing for the calculation of optimized conversion functions to maintain sensor accuracy without the need for standard media calibration, enabling direct calibration in the chemical medium of interest.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration using standard media is performed, then measurement precision is improved, but loss of time increases due to manual removal and reinstallation of the sensor
Solution Approach 1:
The system performs calibration automatically without human intervention. The microprocessor compares sensor readings with stored reference values and autonomously adjusts the conversion function, eliminating the need for manual sensor removal and standard media handling.
Solution Approach 2:
The system performs preliminary calibration during the reference period using known VOC concentrations, storing the resulting conversion function in memory. This pre-computed conversion function is then applied during subsequent measurement periods without requiring repeated manual calibration.
2Measurement precision
If frequent calibration is performed to compensate for sensor drift, then measurement precision is improved, but productivity decreases due to repeated calibration operations
Solution Approach 1:
The calibration process is automated and can be executed at any time without interrupting monitoring operations. The microprocessor automatically compares current sensor readings with reference values and adjusts the conversion function as needed, eliminating downtime associated with manual calibration.
Solution Approach 2:
The system maintains continuous air quality monitoring while performing calibration. The microprocessor can execute calibration routines during normal operation without stopping sensor measurements, ensuring uninterrupted productivity while maintaining precision.
3Measurement precision
If manual calibration procedures are used, then measurement precision is improved, but device complexity increases due to manual intervention requirements
Solution Approach 1:
The entire calibration process is automated through a microprocessor that manages comparison of sensor readings, calculation of conversion functions, and adjustment of measurement parameters. This eliminates manual intervention and reduces operational complexity despite introducing computational complexity.
Solution Approach 2:
The patent replaces manual mechanical calibration operations with an automated electronic system. The microprocessor performs calculations and adjustments that would otherwise require manual intervention, simplifying the overall system operation while maintaining 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 approach simplifies, speeds up, and enhances the reliability of sensor calibration by using a reference sensor to maintain accurate VOC concentration measurements, reducing the need for manual recalibration and ensuring precise readings over time, even in the presence of sensor drift.
Implementation Method 1
A semiconductor sensor, also called a MOX or MOS sensor, consists of a layer of metal oxide heated by a heating element onto which VOCs bind; this phenomenon is known to those skilled in the art as adsorption.
Implementation Method 2
Such a semiconductor sensor also includes electrodes for measuring the electrical conductivity of the metal oxide layer, which is a function of the amount of VOCs adsorbed.
Implementation Method 3
A semiconductor sensor, also called a MOX or MOS sensor, consists of a layer of metal oxide heated by a heating element
Data Source
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AI summary
Disclosed is a method for calibrating a sensor to be calibrated by means of a reference sensor, the sensor to be calibrated being configured to determine a chemical signal based on a conversion function for converting an electrical signal, the reference sensor being configured to determine a reference signal, the method comprising: • measuring (E1, E3), during a reference time period, a first chemical signal (S1P1) and a first reference signal (S2P1) and, during a test period, a second chemical signal (S1P2) and a second reference signal (S2P2), • determining (E2, E4) regression functions (gP1, gP2) defined as follows: S2P1 = gP1(S1P1) and S2P2 = gP2(S2P2), • calculating (E5) a difference (ε) between the regression functions (gP1, gP2) and • when the difference (ε) is greater than a reference difference (εref), determining (E6) an optimised conversion function (f*).