Laser Gas Analyzer Without Reference Cell
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Solution Overview
Problem
Existing laser gas analyzers require a reference gas cell to match the emission wavelength with the absorption wavelength of the gas, which is challenging due to gas leakage, corrosive gas issues, and the need for precise temperature control, and they also face difficulties in environments with dust that can block laser light, increasing equipment costs.
Innovation Solution
A laser gas analyzer design that eliminates the need for a reference gas cell by using a wavelength scanning driving signal to modulate the emission wavelength and a signal processing circuit to detect the frequency-doubled signal for gas concentration measurement, allowing for precise concentration detection without wavelength stabilization and reducing equipment costs by eliminating the need for a dust meter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference gas cell is used to match emission wavelength with absorption wavelength, then measurement precision is improved, but device complexity and cost increase due to temperature control requirements and potential gas leakage issues
Solution Approach 1:
The patent extracts and removes the reference gas cell from the measurement system. Instead of using a separate reference cell to establish wavelength alignment, the system directly measures the absorption spectrum by scanning the laser wavelength across the absorption line, eliminating the need for temperature-controlled reference cells and their associated complexity
Solution Approach 2:
The laser wavelength scanning mechanism serves multiple functions: it both establishes the measurement wavelength range and directly performs the absorption measurement. The single optical path handles both reference and measurement functions simultaneously, eliminating the need for separate reference gas cell systems
2Measurement precision
If a reference gas cell is used for wavelength stabilization, then measurement precision is improved, but reliability deteriorates due to gas leakage and corrosive gas issues
Solution Approach 1:
The reference gas cell is completely removed from the system. Wavelength stabilization is achieved through direct spectral scanning and identification of absorption line positions, eliminating reliability issues associated with sealed gas cells containing corrosive or leaking gases
Solution Approach 2:
Instead of using a physical reference gas cell to copy the absorption characteristics, the system digitally records and analyzes the absorption spectrum shape and position during wavelength scanning, creating a digital reference that avoids all physical gas cell reliability issues
3Adaptability or versatility
If wavelength scanning is performed to measure gas concentration, then adaptability is improved, but device complexity increases due to additional signal processing requirements
Solution Approach 1:
The system uses periodic wavelength scanning at a fixed frequency to modulate the absorption signal. This periodic action allows the use of frequency-doubled synchronous detection to extract the absorption signal from the scanning waveform, simplifying the signal processing by using standard frequency multiplication techniques rather than complex spectral analysis circuits
Solution Approach 2:
The patent replaces complex mechanical wavelength stabilization mechanisms with electronic frequency modulation and digital signal processing. The wavelength scanning is performed electronically through current modulation of the laser, and the absorption signal is extracted through electronic frequency-doubled detection rather than mechanical reference cell adjustments
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 design enables accurate gas concentration measurement with improved precision and reduced costs, as it simplifies the device configuration and stabilizes detection sensitivity, allowing for accurate measurements in environments with dust without the need for additional instruments.
Implementation Method 1
Molecules of a gas are known to each have a characteristic absorption spectrum... the quantity of absorption of laser light with a specific wavelength is proportional to the concentration of the gas being measured
Implementation Method 2
a wavelength scanning driving signal that varies the emission wavelength of a laser element so as to scan the absorption wavelength of the gas for measurement
Implementation Method 3
From the output signal of the light-receiving portion, the signal processing circuit detects a signal of a component at twice the frequency of the modulation signal (the so-called frequency-doubled signal)
Data Source
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AI summary
In a laser gas analyzer using a frequency modulation method, a light source portion 204 comprises a laser driving signal generation portion 204s which combines a wavelength scanning driving signal that varies the emission wavelength of a laser so as to scan the absorption wavelength of the gas for measurement and a high-frequency modulation signal to modulate the emission wavelength, and which outputs the result as a laser driving signal; a current control portion 204c; a laser element 204e; a thermistor 204f; a Peltier element 204g; and a temperature control portion 204d. A signal processing circuit 208 comprises a synchronous detection circuit 208b which detects the amplitude of the frequency-doubled component of the modulation signal from the output signal of a light-receiving portion 207, and a computation portion 208e.