Definition
An infrared gas analyzer is an analytical instrument based on the absorption characteristics of gas molecules to specific wavelengths of infrared radiation. It realizes the quantitative detection of gas concentration by measuring the energy decay of infrared light after it passes through the gas being measured. This technology is suitable for the monitoring of a variety of gas components, especially in industrial process control and environmental monitoring.
Principle
The working principle of infrared gas analyzers is based on Lambert-Beale's law. When infrared light passes through the gas to be measured, the gas molecules selectively absorb infrared radiation at a specific wavelength, and the absorption intensity is directly proportional to the gas concentration. Instruments typically contain an infrared light source, air chamber, filter, and infrared detector. The detector receives the attenuated infrared signal and converts it into an electrical signal, which is processed to calculate the gas concentration value.
The mathematical expression of Lambert-Beale's law is:
I = I0 · e-α·c·L
where I is the intensity of transmitted light, I0is the incident light intensity, α is the absorption coefficient, c is the gas concentration, and L is the light path length.
Measurement method
Common measurement methods include non-spectroscopic infrared and Fourier transform infrared. The non-spectral infrared method uses a narrowband filter to separate characteristic wavelengths, and the structure is relatively simple, which is suitable for conventional gas monitoring. The Fourier transform infrared method obtains a wide band of infrared spectra through interferometers, which can analyze a variety of gas components at the same time, and is suitable for the detection of complex gas mixtures. Both methods require regular calibration with standard gases to ensure measurement accuracy.
Influencing factors
Measurement accuracy is influenced by various factors. Changes in ambient temperature can cause parameter drift in optical components and electronic components, and often there is a temperature compensation mechanism inside the instrument. Gas pressure fluctuations affect the molecular absorption cross-section, and some instruments integrate pressure sensors for real-time correction. Cross-interference can occur when there is a component in the background gas that overlaps with the absorption band of the gas to be measured, which can be reduced by optimizing the filtering wavelength or using multi-wavelength correction techniques. Optical window contamination or dust accumulation can reduce light transmission and require regular maintenance and cleaning.
Application:
In the industrial sector, this instrument is commonly used to optimize combustion processes, monitoring gas composition in flue gases to improve energy efficiency. In environmental monitoring, it is used for continuous observation of specific gas components at air quality monitoring stations. In agricultural research, it can be used to analyze greenhouse gas fluxes. During the chemical production process, the concentration of the reaction gas is monitored in real time to ensure the stability of the process. In the laboratory, it is used as a basic equipment for gas analysis to support materials research and process development.
Selection
Measurement needs should be comprehensively considered when selecting. Clarify the type and concentration range of the gas to be measured, and confirm whether the optical system of the instrument matches the position of the absorption peak of different gas molecules. Choose the appropriate sampling method according to the application scenario, the direct measurement type is suitable for clean gas, and the extraction type can be equipped with a pretreatment system to handle high temperature and high humidity samples. Response time and accuracy need to meet process control or monitoring standard requirements. Examine the instrument's long-term stability, calibration intervals, and ease of maintenance. The working environment conditions such as temperature range and protection level should match the actual installation site. Compliance with relevant industry standards is a basic requirement.