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The Basic Principles and Characteristics of Several Types of Gas Analyzers (2)

The Basic Principles and Characteristics of Several Types of Gas Analyzers (2)

3. Basic principle of infrared gas analyzer (FTIR Gas Analyzer)

(1) Measurement basis of infrared gas analyzer

Lambert-Beer law: Its physical meaning is that when a beam of parallel monochromatic light passes vertically through a uniform non-scattering light-absorbing material, its absorbance is proportional to the concentration of the light-absorbing material and the thickness of the absorbing layer.

(2) Working principle of infrared gas analyzer

It is based on the selective absorption of infrared light by certain gases. The commonly used infrared wavelength of infrared analyzer is 2~12μm.
Simply put, the gas to be measured is continuously passed through a container of a certain length and volume, and a beam of infrared light is injected from the side of one of the two end surfaces of the container that can transmit light. Then measure the intensity of infrared radiation on the other end surface, and finally, the concentration of the gas to be measured can be known based on the absorption of infrared rays and the concentration of light-absorbing substances.

Advantage:
1) Wide measurement range: The upper limit of the gas can be analyzed up to 100%, and the lower limit is up to several (ppm) concentrations. After refined treatment, trace (ppb) analysis (analysis method in which the content of the substance is less than one part per million) can also be carried out;
2) High sensitivity: It has high monitoring sensitivity, and small changes in gas concentration can be distinguished;
3) High measurement accuracy: generally in FS (full scale). Compared with other analysis methods, it has higher accuracy and good stability; fast response speed: the response time is generally within 10S (time to reach T90);

4. The principle of ultraviolet gas analyzer

The ultraviolet gas analyzer is one of the visible spectrophotometers. Its analysis method is ultraviolet absorption spectroscopy, and its working principle is based on the Lambert-Beer law.
Lambert-Beer law A=lg(1/T)=Kbc
Among them, A is the absorbance; T is the transmittance, which is the intensity of the transmitted light compared to the intensity of the incident light; K is the molar absorption coefficient, which is related to the nature of the absorbing substance and the wavelength λ of the incident light; c is the concentration of the absorbing substance; b is Absorbent layer thickness;
When the light source, wavelength, and sample cell thickness are determined, they become constant. At this time, the intensity of light transmitted through the sample is only related to the concentration of the component to be measured in the sample.

Advantages: simple operation, can measure SO2, NOx, HC1, NH3 and other gases.

5. Basic principles of thermal conductivity gas analyzer

Thermal conductivity gas analyzer is a physical gas analyzer. It is based on the principle that different gases have different thermal conductivity, and calculates the content of certain components by measuring the thermal conductivity of the mixed gas.

Advantages: The thermal conductivity analysis instrument is a simple structure, stable performance, low price and relatively mature technology. There are many types of gases applicable and it is a basic analytical instrument.

6. Basic principle of electrochemical gas analyzer

The electrochemical gas analyzer is a chemical gas analyzer. It measures the gas composition based on changes in the amount of ions or changes in current caused by chemical reactions.

In order to improve selectivity, prevent contamination of the measuring electrode surface and maintain electrolyte performance, a diaphragm structure is generally used. Commonly used electrochemical analyzers include positioning electrolysis type and galvanic battery type.

Advantages: small size, fast detection speed, accurate, portable, direct detection and continuous detection on site.

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