Polynomial Approximation for CRDS Gas Measurement Drift
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Solution Overview
Problem
Cavity Ring-Down Spectroscopy (CRDS) apparatuses face measurement value drift due to mirror reflectance changes, position shifts, and thermal expansion, affecting gas concentration accuracy, especially in long-term isotope ratio measurements, and require additional standard gas measurements for calibration, reducing throughput.
Innovation Solution
A gas measurement apparatus and method using a variable-wavelength laser source, optical resonator with high-reflective mirrors, and polynomial approximation of absorption spectra to isolate absorption peak coefficients, eliminating the need for standard gas measurements and improving measurement accuracy by reducing drift influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cavity ring-down absorption spectroscopy is used to improve detection sensitivity by lengthening the effective optical path length, then measurement sensitivity is improved, but measurement value drift occurs due to mirror reflectance changes and thermal expansion
Solution Approach 1:
The patent applies parameter changes by measuring the ring-down time at multiple different wavelengths and using polynomial approximation to extract the absorption peak coefficient. This transforms the measurement approach from a single-wavelength absolute measurement to a multi-wavelength relative measurement, where the absorption coefficient is derived from the curvature of the polynomial fit rather than absolute ring-down time values, thereby eliminating drift effects.
Solution Approach 2:
The patent replaces the traditional mechanical/optical alignment system that relies on precise mirror positioning and perpendicularity with a computational approach. Instead of mechanically ensuring perfect alignment, the system uses polynomial approximation of multi-wavelength ring-down time data to mathematically extract the absorption coefficient, substituting physical precision requirements with mathematical processing.
2Measurement precision
If standard gas measurements are performed periodically for calibration to correct drift, then measurement accuracy is maintained, but measurement throughput decreases due to additional measurement time
Solution Approach 1:
The patent implements self-service by enabling the measurement system to automatically compensate for its own drift without requiring external calibration standards. The multi-wavelength polynomial approximation method allows the system to self-correct measurement values by extracting absorption coefficients from the curvature of ring-down time variations across wavelengths, eliminating the need for periodic standard gas injections.
Solution Approach 2:
The patent extracts the absorption coefficient information from the curvature of the polynomial fit to ring-down time data, separating the useful measurement information from the drift-affected absolute values. By taking out only the relevant curvature information through polynomial approximation, the system obtains accurate concentration measurements without requiring absolute calibration.
3Measurement precision
If the wavelength range for measurement is expanded to capture the full absorption peak, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent applies partial action by measuring ring-down times at a discrete set of wavelengths distributed across the absorption feature rather than continuously scanning the entire spectrum. The polynomial approximation then reconstructs the full absorption peak shape from these partial measurements, achieving accurate peak detection with fewer measurement points and reduced measurement time.
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 method allows for high-accuracy gas concentration calculations without additional standard gas measurements, reducing measurement time and maintaining throughput by isolating absorption peak coefficients from drift factors, effectively addressing short-term and long-term measurement value fluctuations.
Implementation Method 1
the wavelength (frequency) of light that may resonate is determined in accordance with a resonance condition... When the oscillation frequency of the laser light in the laser-light source 1 is adjusted to coincide with the mode frequency, the power of the light is accumulated in the optical resonator 4
Implementation Method 2
the light is gradually absorbed by a component of a measured gas contained in the measurement cell 40 and becomes attenuated
Implementation Method 3
a photodetector detects the intensity of the light obtained by being absorbed by a gas component... the photodetector 5 repeatedly detects a portion of the attenuating light
Data Source
AI summary
According to an aspect of the present invention, a gas measurement apparatus includes a measurement controller (6), a spectrum generator (72), a processing unit (73), and a result obtaining unit (74). The measurement controller (6) controls the apparatus so that a laser-light source (1) causes laser light to be incident to an optical resonator (4) and a wavelength of the laser light is scanned within a predetermined wavelength range, the range including an absorption peak of a target component, thereby performing a CRDS measurement. The spectrum generator (72) generates an absorption spectrum based on data obtained at each wavelength within a predetermined wavelength range. The processing unit (73) approximates a waveform shape of the absorption peak of the target component in the absorption spectrum with a polynomial and acquires a coefficient of a term of a predetermined degree in the polynomial. The result obtaining unit (74) obtains absorption intensity from the coefficient, based on predetermined reference information indicating a correspondence relation between a coefficient of the term of the predetermined degree and the absorption intensity.