GB 5275-1985 Gas analysis - Preparation of mixed gases for calibration - Permeation method GB5275-1985 standard download decompression password: www.bzxz.net

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National Standard of the People's Republic of China
Gas analysis-Preparation of catibration gas mixtures--Permeation methodUDC 543.27
:53.089.68
GB 5275-85
This standard describes the preparation of calibration gas mixtures using the permeation principle, which is a dynamic gas distribution method. The concentration range of the required components in the mixed gas is 10-°～10-5 (volume ratio), and the accuracy of the component concentration can reach 2%. In fact, the concentration unit can also be expressed in micrograms/cubic meters. Since it is difficult to keep the concentration of the mixed gas stable within such a low concentration range, the calibration mixed gas must be prepared immediately before use, and the pipeline for conveying the mixed gas should be as short as possible. This standard is equivalent to the international standard ISO6349-1979 "Gas analysis-Preparation of mixed gas for calibration-Permeation method". 1 Principle
The principle of the method is based on the component gas (SO2, NO, NH, etc.) in the permeation tube to penetrate into the carrier gas flow through an appropriate membrane, and the carrier gas is the background gas constituting the mixed gas. The permeation tube* contains pure component substances (see clause 2 for details). - A carrier gas controlled to a known flow rate flows partially or completely through the permeation tube. It plays the role of carrying the permeated component gas molecules. The carrier gas should be a gas that has been processed to be very pure, especially it is not allowed to contain trace amounts of component gases, and those gases that do not interact with the materials constituting the permeation tube should be selected. The permeation rate through the permeation membrane** depends on the properties of the component substances themselves, the structure and area of ​​the permeation membrane, the temperature, and the partial pressure difference of the gas inside and outside the tube. These factors can be kept constant as long as the permeation tube is operated correctly.
According to the current state of knowledge, there is no formula that accurately describes this permeation phenomenon. If the permeation rate remains constant, the permeation rate of the permeation tube can be determined by weighing at appropriate time intervals [other methods besides weighing are listed in Appendix A (reference), but are not part of this standard). Considering that various parameters affect the permeation rate, the following requirements must be met for a permeation tube containing a substance of known composition: a. The temperature of the permeation tube should be kept constant between two weighings; b. The permeation tube should be continuously purged with a carrier gas flow to keep the component partial pressure outside the permeation tube small enough to be ignored; c. The gas pressure inside the permeation tube should be kept constant between two weighings, that is, there must be liquid component substances in the permeation tube, or the amount of component substances in the permeation tube is much greater than the amount lost due to permeation. The concentration of the prepared calibration gas mixture, °C, is a function of the permeability of the permeation tube and the background gas flow rate, given by the following formula: CWww.bzxZ.net
Where: 9m——permeability (mass flow rate) of the calibration component under given conditions; Q——background gas flow rate (expressed in appropriate units). *Tube refers to the container and the substance it contains, regardless of its shape (except 2.3.4). **ISO6349 originally used "diffusion" in this article. Issued by the National Bureau of Standards on August 1, 1985
Implementation on June 1, 1986
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