Multi-Frequency Wavelength Modulation Gas Analyzer Signal Processing
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Solution Overview
Problem
The existing gas analyzers, such as laser spectrometers, face limitations in measurement signal-to-noise ratio due to noise interference in the measurement signal, which restricts the detection and determination limits for gas component concentrations.
Innovation Solution
The method involves modulating the wavelength of the light source with multiple frequencies (2n-1)f, demodulating the measurement signal at the second harmonic 2(2n-1)f, and combining these signals through data fusion or individual evaluation to enhance the signal-to-noise ratio by separating frequency components and minimizing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the wavelength of light is modulated with a single frequency for measurement, then the measurement process is simple, but the signal-to-noise ratio is limited due to noise interference
Solution Approach 1:
The single modulation frequency is segmented into multiple modulation frequencies (first, second, third frequencies). Each frequency component is demodulated separately to extract measurement signals, which are then combined to achieve superior noise rejection and improved signal-to-noise ratio while maintaining measurement accuracy
Solution Approach 2:
The measurement process transitions from a single-frequency dimension to a multi-frequency dimensional approach. By modulating with multiple frequencies and demodulating at corresponding harmonics, the system exploits the frequency dimension to separate signal from noise, achieving better measurement precision without excessive complexity
2Measurement precision
If multiple modulation frequencies are used to improve signal-to-noise ratio, then measurement precision improves, but device complexity increases
Solution Approach 1:
The system employs periodic modulation at multiple distinct frequencies, where each frequency component can be independently demodulated using standard lock-in amplification techniques. This periodic structure allows for systematic signal separation and combination, improving precision while keeping the complexity manageable through established periodic signal processing methods
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 significantly improves the signal-to-noise ratio by utilizing non-correlated noise in different frequency bands, resulting in a more accurate measurement of gas component concentrations with reduced interference.
Implementation Method 1
A wavelength-tunable light source in the form of a laser diode generates light in the infrared range, which is guided through a process gas to be measured (measuring gas) and then detected. The wavelength of the light is tuned to a specific absorption line of the gas component to be measured, with the laser diode periodically scanning the absorption line depending on the wavelength.
Implementation Method 2
The wavelength of the light is tuned to a specific absorption line of the gas component to be measured. Since the profile of the absorption line is not linear, harmonics above the modulation frequency are also generated in the measurement signal obtained during detection.
Implementation Method 3
A wavelength-tunable light source in the form of a laser diode generates light in the infrared range, which is guided through a process gas to be measured (measuring gas) and then detected.
Data Source
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AI summary
For wavelength-dependent sampling of an absorption line of a gas component to be measured in a sample gas (1), the wavelength of the light (4) from a wavelength-tunable light source (3) is varied within periodically successive sampling intervals and additionally modulated with a frequency (f). The modulated light (4) is guided through the sample gas (1) to a detector (5), whose measurement signal (14) is demodulated at the second harmonic (2f) of the modulation frequency, and the resulting demodulated measurement signal (142f) is evaluated for each sampling interval to obtain a measurement result (262f). To improve the signal-to-noise ratio, the wavelength of the light (4) from the light source (3) is additionally modulated with at least one further frequency (3f, 5f, 7f) that is twice the modulation frequency higher than the next lower further frequency or the modulation frequency.The measurement signal (14) is additionally demodulated at the second harmonic (6f, 10f, 14f) of at least one further frequency (3f, 5f, 7f). The resulting at least one further demodulated measurement signal (146f, 1410f, 1414f) is either combined with the demodulated measurement signal (142f) or evaluated to produce a further measurement result (266f, 2610f, 2614f), which is then combined with the measurement result (262f).