Wavelength Modulation Spectroscopy Apparatus for Gas Concentration Analysis
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Solution Overview
Problem
Conventional WMS methods face challenges such as signal drift due to laser intensity variations, require high-response-speed detectors, and complex calculations for interference removal, especially in the mid-infrared region, making gas analysis costly and complex.
Innovation Solution
An analysis apparatus that calculates the intensity ratio logarithm of measurement target and reference light, extracts frequency components at multiples of the modulation frequency, and uses these to directly quantify the concentration of the target component, eliminating the need for high-response-speed detectors and complex calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavelength modulation spectroscopy is used to increase detection sensitivity, then measurement precision is improved, but device complexity increases due to requirements for high-response-speed detectors and complex calculation processes
Solution Approach 1:
The patent changes the detection parameter from direct intensity measurement to measurement of frequency components (specifically the second harmonic component at 2ω). By detecting the amplitude of the 2ω component in the lock-in amplifier, the system achieves high sensitivity without requiring detectors with extremely high response speeds, thus resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent employs periodic modulation of the laser wavelength at frequency ω, which generates a periodic absorption signal containing the second harmonic component at 2ω. This periodic action allows the use of lock-in detection to extract the weak absorption signal from noise, achieving high sensitivity while using standard detectors rather than specialized high-speed detectors
2Measurement precision
If wavelength modulation spectroscopy is used to increase detection sensitivity, then measurement precision is improved, but device complexity increases due to complex calculation processes for spectrum analysis
Solution Approach 1:
The patent extracts only the essential information (amplitude of the 2ω frequency component) from the modulated absorption signal using lock-in detection. This extraction approach eliminates the need for complex full-spectrum analysis, baseline correction, and fitting calculations, thereby reducing computational complexity while maintaining high measurement precision
Solution Approach 2:
The patent replaces complex computational processing with a simpler detection mechanism. By using lock-in amplification to directly measure the 2ω component amplitude, the system substitutes complex mathematical operations (spectrum calculation, baseline estimation, multivariate analysis) with a straightforward electrical measurement process
3Reliability
If reference light intensity monitoring is added to suppress drift, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent introduces a reference light path that serves as an intermediary to monitor laser intensity variations. The reference detector measures the intensity of light that has not interacted with the sample, providing a reference signal that compensates for drift in the measurement channel. This intermediary reference path enables reliable drift suppression without requiring complex real-time correction algorithms or additional active control components
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 allows for accurate gas component analysis with a simple, cost-effective configuration, reducing the impact of laser intensity variations and interference, and enabling precise concentration measurement using low-response-speed detectors in the mid-infrared region.
Implementation Method 1
analysis such as gas component analysis... obtain the absorption spectrum of measurement target gas... light whose wavelength is modulated... detect the intensity of measurement target light that is light after the reference light has transmitted through the sample
Data Source
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AI summary
The present invention allows an analysis apparatus utilizing light absorption to accurately measure the absorbance or concentration of a measurement target component with simple calculation while eliminating effects such as the effect of a variation in light source intensity and the effect of interference by another substance. The present invention is adapted to include: a light source (2) adapted to emit reference light that is light whose wavelength is modulated at a predetermined modulation frequency; a light detector (3) adapted to detect the intensity of measurement target light that is light after the reference light has transmitted through the measurement target component, and the intensity of the reference light; a first calculation part (61) adapted to calculate an intensity ratio logarithm that is the logarithm of the ratio between the intensity of the measurement target light and the intensity of the reference light; a frequency component extraction part (62) adapted to lock-in detect the intensity ratio logarithm with a reference signal having a frequency n times (n is an integer equal to or more than 1) the modulation frequency; and a second calculation part (63) adapted to, on the basis of the result of the detection by the frequency component extraction part (62), calculate the concentration or absorbance of the measurement target component.