Gas Detection Etalon Fringe Suppression via 3-Point Measurement
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Solution Overview
Problem
Existing gas detection methods using wavelength modulation laser spectrometry are limited by etalon fringes, which are sensitive to temperature and wavelength changes, leading to reduced accuracy and detection limits due to residual etalon fringe noise.
Innovation Solution
A 3-point measurement technique is employed, where pre-measuring signals are obtained at the center and off-peak positions of the gas absorption peak with respect to the DC drive current, and the final measuring signal is calculated as the difference between these signals, effectively canceling out residual etalon fringe contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavelength modulation laser spectrometry is used for gas detection, then gas concentration can be measured, but residual etalon fringe noise reduces measurement accuracy and detection limits
Solution Approach 1:
The patent extracts and removes the harmful etalon fringe noise from the measurement signal by using a reference channel that measures only the etalon fringes without gas absorption. The gas concentration measurement is then obtained by subtracting the reference channel signal from the main measurement channel, effectively taking out the harmful etalon fringe component.
Solution Approach 2:
The patent introduces a reference channel as an intermediary measurement path that contains the etalon fringes but excludes the gas absorption signal. This reference channel acts as a mediator to separate and eliminate the harmful etalon fringe noise from the main measurement, improving the accuracy of gas concentration detection.
2Device complexity
If single-channel detection is used, then device complexity is reduced, but etalon fringe noise cannot be eliminated
Solution Approach 1:
The patent segments the detection system into two functional channels: a main measurement channel that captures both gas absorption and etalon fringes, and a reference channel that captures only etalon fringes. This segmentation allows the harmful etalon fringe noise to be isolated and removed through signal subtraction, improving measurement accuracy while maintaining relatively simple device structure.
3Stability of the object's composition
If temperature stabilization is strictly controlled, then wavelength drift is minimized, but device complexity and cost increase
Solution Approach 1:
The patent employs a self-service approach where the system automatically compensates for temperature-induced wavelength drifts by using the reference channel to measure and subtract the resulting etalon fringe variations. This eliminates the need for complex active temperature stabilization systems, as the measurement method itself compensates for thermal effects.
Solution Approach 2:
The reference channel provides real-time feedback on etalon fringe variations caused by temperature drifts. This feedback is used to correct the main measurement signal through subtraction, creating a closed-loop compensation mechanism that maintains measurement accuracy without requiring active temperature control.
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 technique enhances the stability of gas detection devices against temperature variations and reduces the impact of etalon fringes, allowing for more accurate gas concentration measurements with improved detection limits and faster measurement cycles.
Implementation Method 1
Gas detection method and device for determining a precise gas concentration value... uses the fact that the modulation of the wavelength is directly connected to a modulation of the laser source output intensity... the intensity of the light having passed the gas volume and being incident to the detector therefore shows a first modulation related to the laser source intensity and a second modulation related to the gas absorption
Implementation Method 2
A light sensor respectively is arranged at the periphery of a detection region intended for receiving at least a gas the concentration of which is to be determined. The light sensor receives a resulting light signal formed by the initial light signal having passed through the detection region.
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The invention proposes a method for etalon suppression in a gas detection device by determining an etalon fringe period during a calibration step without gas in dependency of the DC drive current. A measuring signal which is a function of the gas absorption and substantially independent of an intensity modulation of an initial light signal at an initial frequency (f) is generated by determining a first pre-measuring signal when the laser source is operated at the center of the gas absorption peak, a second pre-measuring signal when the laser source is operated with a DC drive current below the gas absorption peak of the gas to be detected, and a third pre-measuring signal when the laser source is operated with a DC drive current above said gas absorption peak, with a difference between said DC drive currents which corresponds to the etalon fringe period determined in a calibration step before. The final measuring signal is determined as the difference between the first pre-measuring signal and the arithmetic mean of the second pre-measuring signal and the third pre-measuring signal. This etalon fringe suppression allows to implement a substantial simplification of a reference channel in a gas detector, which does not require separate lock-in channels which analyse the detector signal either on the modulation frequency (f), or on twice the modulation frequency (2f).