Multi-Gas NDIR Detection for Overlapping Absorption Bands
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Solution Overview
Problem
Conventional NDIR gas detection systems face challenges in accurately identifying and quantifying multiple gases with overlapping absorption bands due to the lack of effective methods for distinguishing between them, particularly in the 3.8 to 4.1 μm gap where light is not absorbed by gases of interest.
Innovation Solution
The system employs a method of irradiating a sample volume with light at a reference wavelength and test wavelengths modulated out of phase with the reference wavelength, using a sensing system that includes a controller to compare intensity differences over time, and optionally uses a calibration system with a reference vial to adjust light intensities, along with an optical system utilizing dichroic mirrors and collimators to filter and modulate light for precise detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NDIR gas detection systems use a single reference wavelength (3.95 μm) to detect gases, then the system structure is simple, but it cannot accurately distinguish between multiple gases with overlapping absorption bands
Solution Approach 1:
The patent segments the optical detection system into multiple independent wavelength channels, each targeting specific gas absorption bands. Instead of using a single reference wavelength, the system divides the infrared spectrum into multiple bands (e.g., 3.3 μm for methane, 4.3 μm for CO2, 2.35 μm for CO) with dedicated light sources and detectors for each, enabling simultaneous multi-gas detection without cross-interference
Solution Approach 2:
The patent transitions from one-dimensional single-wavelength detection to multi-dimensional spectral detection by introducing multiple wavelength dimensions. Each gas type is detected at its characteristic absorption wavelength, creating a spectral fingerprint approach that resolves the ambiguity of overlapping absorption bands through dimensional expansion of the detection space
2Measurement precision
If the system uses multiple light sources and detectors for different wavelengths to distinguish overlapping absorption bands, then gas identification accuracy improves, but the device complexity increases
Solution Approach 1:
The patent implements universal detection components that serve multiple functions. The controller integrates data processing for all wavelength channels, the optical bench provides a common mounting platform for all light sources and detectors, and the housing structures accommodate the entire multi-wavelength system, reducing overall complexity despite multiple detection channels
Solution Approach 2:
The patent merges multiple detection functions into an integrated system where multiple light sources operate simultaneously on a common optical path, detectors collect signals from multiple wavelengths, and a single controller processes all data to identify multiple gases, reducing the need for separate detection systems for each gas type
3Adaptability or versatility
If the system irradiates the sample volume with multiple lights at different test wavelengths to detect different analyte gases, then the detection capability for multiple gases improves, but the calibration complexity increases
Solution Approach 1:
The patent performs preliminary calibration by irradiating a reference cell with known gas concentrations at all test wavelengths before field deployment. The controller stores reference absorption characteristics for each gas type at each wavelength, enabling rapid field calibration without requiring complex real-time adjustments during actual gas detection operations
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 enables accurate identification and quantification of multiple gases, including noxious gases like carbon monoxide and hydrocarbons, by effectively distinguishing between gases with overlapping absorption bands, even in remote environments, ensuring reliable gas detection and measurement.
Implementation Method 1
Different types of gases have unique light absorption characteristics. In other words, each gas type absorbs different optical frequencies.
Implementation Method 2
The Beer-Lambert law, which can be expressed as I=I0e−σnl, generally, defines a relationship that relates the absorption of a light to properties of the material irradiated by the light
Implementation Method 3
an optical system, which includes a light source, dichroic mirrors, optical filters, collimators
Data Source
AI summary
A non-dispersive near infrared light is used for detecting analyte gases in a testing zone. A sample obtained from the testing zone is irradiated with a reference light and with test lights. The test lights are emitted in sequence and modulated to be out of phase with the reference light. Frequencies of the test lights are in the absorption bands of particular analyte gases, with the reference light frequency being outside of the absorption bands. Analyte presence in the sample is identified by sensing changes in differences over time of test light and reference light intensity. Before irradiating the sample, the lights are optically conditioned by aligning them on the same path, and splitting the bandwidth of some lights for detecting analytes with overlapping absorption bands.