Variable Attenuator for Laser Gas Analysis in Sooty Combustion
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Solution Overview
Problem
Laser absorption spectroscopy systems face challenges in accurately analyzing combustion gases containing high concentrations of soot and dust, as the attenuation of laser light leads to reduced accuracy and saturation issues with photodetectors, making it difficult to analyze gases with varying concentrations of soot and dust.
Innovation Solution
A gas analysis system incorporating a variable light attenuator controlled by an attenuation amount controller, which adjusts the light attenuation based on the transmitted light amount detected by a photodetector, ensuring accurate analysis of combustion gases with high or low soot and dust concentrations by maintaining optimal laser light intensity for the photodetector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser light is transmitted through combustion gas with high soot and dust concentration, then measurement can be performed in severe environment, but light attenuation exceeds 90% making detection difficult
Solution Approach 1:
The patent applies dynamics by making the light source intensity adjustable and the optical path length variable. The light source can dynamically increase its output when high attenuation is detected, and the optical path length can be adjusted to optimize the balance between measurement representativeness and light intensity at the detector.
Solution Approach 2:
The patent changes parameters including light source intensity, optical path length, and detector sensitivity. By adjusting these parameters dynamically based on measured attenuation levels, the system maintains optimal detection conditions across varying soot and dust concentrations.
2Measurement precision
If photodetector sensitivity is increased to detect highly attenuated light, then detection capability in high soot environments improves, but saturation occurs when soot concentration is low
Solution Approach 1:
The photodetector sensitivity is made dynamically adjustable rather than fixed. The system automatically adjusts the detector gain or sensitivity level based on the measured light attenuation, ensuring optimal detection across both high and low soot concentration conditions without saturation.
Solution Approach 2:
The system employs feedback control where the measured light intensity is used to adjust detector sensitivity. When attenuation is high, the detector sensitivity is increased; when attenuation is low, sensitivity is reduced to prevent saturation, maintaining optimal measurement conditions dynamically.
3Device complexity
If fixed optical path length is used, then device structure is simple, but accurate measurement across varying soot concentrations cannot be achieved
Solution Approach 1:
The optical path length is made variable rather than fixed, allowing dynamic adjustment to compensate for varying light attenuation caused by different soot and dust concentrations, thereby maintaining measurement accuracy across different operating conditions.
Solution Approach 2:
The system changes the optical path length parameter dynamically based on measured attenuation levels. When attenuation is high, the path length is shortened to maintain sufficient light intensity; when attenuation is low, the path length can be extended to improve measurement representativeness.
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
The system enables accurate analysis of combustion gases with varying soot and dust concentrations by dynamically adjusting light attenuation, maintaining high detection accuracy and sensitivity, even in environments with significant light attenuation.
Implementation Method 1
The tunable diode laser absorption spectroscopy (TDLAS) is a particularly promising technique for measuring the composition and temperature of combustion gas and other combustion parameters. In each of the above techniques, light is conducted through a combustion process chamber, and is absorbed in a specific spectral band that uniquely corresponds to a gas that exists in the process chamber
Implementation Method 2
using laser light makes it possible to achieve a high luminance required to realize transmission which can be detected even under such attenuation. To bear the harsh condition of a target usage more suitably, laser light may be sent into a target environment through protected optical fiber
Data Source
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AI summary
A gas analysis system is provided with: a laser light source for emitting laser light that is transmitted through a gas to be analyzed; a photodetector that is configured so as to receive laser light transmitted through the gas to be analyzed and that is for outputting a signal corresponding to the emission intensity of the received laser light; a gas analysis device for analyzing the gas to be analyzed on the basis of the signal output from the photodetector; a variable optical attenuator that is provided between the gas to be analyzed and the laser light source; a transmitted light amount detector that evaluates the transmitted light amount of the laser light transmitted through the gas to be analyzed on the basis of the signal output from the photodetector; and an attenuation amount control device that controls the attenuation amount of the variable optical attenuator on the basis of the transmitted light amount of the laser light evaluated by the transmitted light amount detector.