Optical Gas Sensor Temperature Calibration
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Solution Overview
Problem
Optical absorption gas sensors with LEDs and photodiodes face challenges in accurately measuring analyte gas concentrations due to temperature variations between the LED and photodiode, making it difficult to independently calibrate their optical properties and requiring them to be mounted close together for thermal equilibrium, which limits design freedom and increases costs.
Innovation Solution
A method for calibrating optical absorption gas sensors involves measuring photodiode and LED output signals at different concentrations and temperatures, allowing for the separation of temperature effects on each component, enabling accurate compensation for temperature variations without requiring them to be at the same temperature, thus allowing greater design flexibility and cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the LED and photodiode are mounted close together to maintain thermal equilibrium, then temperature compensation is simplified, but design freedom is constrained and manufacturing costs increase
Solution Approach 1:
The patent divides the temperature calibration into separate independent calibrations for the LED and photodiode. The LED is calibrated at multiple temperatures to determine its optical property variations, and the photodiode is independently calibrated to determine its response variations. This segmentation allows the components to be mounted at different locations without requiring thermal equilibrium, thus resolving the contradiction between simplified temperature compensation and design freedom.
2Device complexity
If the LED and photodiode are mounted close together for thermal equilibrium, then a single temperature measurement suffices, but the components cannot be positioned independently for optimal performance
Solution Approach 1:
The patent implements separate temperature measurements for the LED and photodiode using independent temperature sensors. Each component's temperature is measured and compensated for independently through separate calibration data. This allows the components to be positioned independently for optimal optical and thermal performance while maintaining accurate temperature compensation, resolving the contradiction between device complexity and component positioning flexibility.
3Measurement precision
If independent calibration of LED and photodiode temperature effects is performed, then accurate compensation is achieved, but the calibration procedure becomes complex requiring independent temperature control
Solution Approach 1:
The patent performs preliminary independent calibration of the LED and photodiode during manufacturing. The LED is calibrated at multiple predetermined temperatures to store calibration data characterizing its optical property variations. The photodiode is independently calibrated to store data characterizing its response variations. These preliminary calibrations enable accurate temperature compensation during operation without requiring complex real-time independent temperature control, resolving the contradiction between measurement precision and ease of manufacture.
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 more accurate and energy-efficient gas sensors with greater design freedom, as the temperature effects on the photodiode and LED can be independently distinguished and compensated for, allowing the components to be positioned further apart and reducing manufacturing costs.
Implementation Method 1
an LED (for example, an infra-red LED) as a source of light
Implementation Method 2
The concentration of an analyte gas in the gas sample can be determined from the absorption of light by the analyte gas
Implementation Method 3
a photodiode as a detector of light
Data Source
AI summary
An optical absorption gas sensor has an LED light source and a photodiode light detector, a temperature measuring device for measuring the LED temperature and a temperature measuring device for measuring the photodiode temperature. The sensor is calibrated by measuring the response of photodiode current at zero analyte gas concentration and at a reference analyte gas concentration. From these measurement, calibration data taking into account the effect of photodiode temperature on the sensitivity of the photodiode and, independently, the effect of changes in the spectrum of light output by the LED on the light detected by the photodiode with LED temperature can be obtained. Calibration data is written to memory in the gas sensor and in operation of the gas sensor, the output is compensated for both LED and photodiode temperature. The LED and photodiode can therefore be relatively far apart and operate at significantly different temperatures allowing greater freedom of optical pathway design.