Infrared gas analyzer principle

Infrared gas analyzers use infrared gas for gas analysis. It is based on different concentrations of the components to be analyzed and the absorbed radiant energy is different. The remaining radiant energy causes the temperature in the detector to rise differently, and the pressure on both sides of the rotor film is different, thereby generating an electrical signal of the capacitive detector. In this way, the concentration of the component to be analyzed can be measured indirectly.

1. Beer's Law infrared gas analyzer is made according to Beer's law. Assume that the gas to be measured is an infinitely thin plane. The infrared light of intensity k penetrates it vertically, the amount of energy attenuation is: I=I0e-KCL (Beer's law)

Where: I - radiation intensity absorbed by the medium;

I0—radiation intensity before infrared rays pass through the medium;

K--absorption coefficient of the component to be analyzed for radiation;

C--the gas concentration of the component to be analyzed;

L--air chamber length (thickness of measured gas layer)

For a well-established infrared gas analyzer, the measured composition is fixed, that is, the absorption coefficient of the component to be analyzed for the radiation band k is fixed; the infrared source is fixed, that is, the radiation intensity I0 before the infrared ray passes through the medium is certain; Room length L is certain. It can be seen from Beer's law that the concentration C of the component to be analyzed can be determined by measuring the attenuation I of the radiation energy.

2. Analytical detection principle The infrared gas analyzer generates two infrared rays from two independent light sources, respectively. The beam passes through the modulator and becomes a 5 Hz beam. According to actual needs, the radiation can be reduced by a filter to reduce the interference of other infrared-absorbing gas components in the background gas.

Infrared rays pass through two gas chambers, one is a measuring chamber filled with the gas to be measured flowing continuously, and the other is a reference chamber charged with a background gas having no absorption properties. During operation, when the concentration of the measured gas in the measurement chamber changes, the amount of infrared light absorbed changes correspondingly, and the amount of light of the reference beam (reference chamber beam) does not change. The difference in the amount of light exiting the second chamber passes through the detector, causing the detector to produce a pressure difference and become an electrical signal of the capacitive detector. This signal is amplified by the signal conditioning circuit and sent to the display and the master control's CRT display. The size of this output signal is proportional to the concentration of the buried component.

The detector we use is a thin-film microphone. The receiving chamber is filled with the component to be abyss in the sample gas. The two receiving chambers are separated by a thin metal film. When the two measuring pressures are different, the membrane can be deformed to displace, and a fixed circle is placed on one side of the membrane. Disk electrode. The movable diaphragm and the fixed electrode form the two poles of a capacitive converter. The entire structure maintains a tight seal. The gases in the two receiving chambers are separated by a moving film, but a small hole a few hundredths of a millimeter in size is placed on the structure so that the gases on both sides are statically balanced. The radiation beam passes through the reference chamber and the measurement chamber and enters the detector's receiving chamber. As the gas in the receiving chamber absorbs, the temperature of the gas increases, the thermal motion of the gas molecules increases, and the pressure generated by the resulting thermal expansion increases. When the measurement room is filled with zero point gas (N2), the light energy from the two chambers is balanced, the pressures on both sides are equal, the moving film is maintained at the equilibrium position, and the detector output is zero. When the sample chamber is connected to the sample gas, the light energy entering the receiving chamber at the measuring edge is lower than the reference edge, so that the pressure at the measuring edge is reduced, and the film is displaced. Therefore, the distance between the two plates is changed, and the electricity is changed. Capacity C.

Infrared gas analyzer can be used to analyze a variety of polyatomic gases, such as: C2H2, C2H4, C2H5OH, C3H6, C2H6, C3H8, NH3, CO2, CO, CH4, SO2 and so on. It cannot be used to analyze polyatomic gases and inert gases composed of the same kind of atoms, such as: N2, Cl2, H2, O2, and He, Ne, Ar, etc.