Discussion on Difficulties in Application of Online Gas Analyzer

　　Gas analyzer is a tool used to analyze and test gas components. With it, data on the types and contents of certain components can be obtained. However, gas analyzer is not a simple tool. It is not as simple in structure as flow meter and pressure gauge, nor as easy to operate and use as various thermal instruments . It is a tool with complex structure and difficult to use technology. Using gas analyzer is a complex and difficult to master specialized technology.

　　Generally speaking, the application of gas analysis instruments is a unique technical work and a research-based work, but this is not known and understood by outsiders. The difficulties in the application of gas analysis instruments can be roughly understood from the following aspects.

　　Gas analysis is a series of chemical processes

　　A gas analyzer or a gas analysis system is equivalent to a complete set of chemical process equipment. Therefore, the working process of the gas analysis instrument system is to realize a series of chemical processes. If you want to get correct data through gas analysis, you must understand the situation and changes in each stage of this series of chemical processes, carefully study and grasp the laws, only in this way can you achieve the purpose of correct measurement. It should be pointed out that not only does a gas analyzer have the same situation and conditions of a set of chemical process, but sometimes the sample gas pretreatment part (including sampling system) at the front stage of the instrument is also a set of chemical process. If you encounter more complex and special process technology conditions, then the chemical process reflected by the sample gas pretreatment system is still very complex, equivalent to the purification process of a small chemical plant. It can be seen that the process of gas analysis is to strictly control various factors that affect the measurement conditions under the condition of understanding and grasping the conditions of the entire chemical process system, so as to obtain the correct data required by the process and management staff.

　　It is difficult to control influencing factors and eliminate interference factors during application

　　In the process of instrument application, there are many kinds of influencing factors and the changes are more complicated. It is difficult to effectively control these influencing factors and eliminate the factors that interfere with the measurement. For example, for the determination of trace oxygen, not only the system material and sealing must be strictly controlled, but also many factors such as the cleanliness of the system must be solved one by one, otherwise, the oxygen component analysis will not get the correct measurement results. For the determination of trace water content in gas, in addition to considering the various influencing factors mentioned above, the adsorption equilibrium problem of water in the sample gas in the pipeline must also be considered. The proper handling of this problem must rely on repeated experiments, understand its changes and laws, and grasp the manipulation technology in order to obtain correct results. Of course, the factors to be considered and controlled when using gas chromatograph to determine the ppm-ppb level impurity content in high-purity gas are even more complicated.

　　The factors affecting trace gas composition analysis are more complex

　　The microscopic changes that occur when gas components move in pipelines and equipment are complex and changeable. Many influencing factors that can be ignored in the analysis of constant gas components cannot be ignored in the analysis of trace gas components, but must be taken seriously. At this time, these factors have become the main contradictions that affect the correct results of trace gas component analysis. They must be eliminated and resolved one by one to ensure the smooth operation of the trace gas analysis instrument. These influencing factors mainly include the following aspects:

　　① Repeated mixing of gases in the sampling pipeline;

　　②Physical and chemical effects between the tube wall and gas components;

　　③ Pipe material;

　　④Pipeline connection method;

　　⑤Pipeline cleanliness.

　　Instrument and method validation is one of the keys to obtaining correct data

　　As a measurement and testing tool, the instrument, under normal operation, gives mostly relative values ​​of data. The instrument itself cannot provide or verify whether the measured data is correct and the degree of correctness (accuracy). It must be completed by peripheral technical work, which is the verification of analytical data.

(1) Verification of the linear relationship of the instrument . First of all, to ensure the normal operation of the instrument, the analytical instrument , as a kind of measuring instrument, must be tested every year by the authoritative measurement department in accordance with the regulations formulated by the state before it can be allowed to be used. At the same time, it is also necessary to use a series of standard gases every year to check whether the linear relationship of the instrument in the entire linear range remains normal. Otherwise, blindly believing in the integrity of the analytical instrument (even if it is an imported instrument) will definitely result in erroneous data and lead to mistakes in production management and quality management.

　　(2) Error analysis. In the application process of analytical instruments, error analysis must be conducted for each measurement result to determine the authenticity, reliability and credibility of the data analysis. A qualified analyst will not and should not report or publish the results of each analysis and measurement carelessly. Generally, after the measurement results are obtained, after error analysis, when it is determined that the sum of the errors of the analysis data is less than the specified allowable error, this data (or a group of data) will be considered as the correct measurement result and reported or published. Otherwise, incorrect data will bring serious adverse consequences to production managers.

　　(3) Calibration of instruments commonly used in quantitative analysis. As a quantitative analysis instrument, the gas analyzer must be calibrated (or calibrated) with standard gas before quantitative analysis. Standard gas is generally purchased from the national metrology department or a legitimate factory. In special cases, it can also be configured by yourself (but you must have the qualifications and ability to configure standard gas and related equipment). The shelf life of standard gas is one year. When using standard gas to calibrate analytical instruments, you must also have a deep understanding of the normal procedures and usage rules. If you purchase and use standard gas that does not meet the requirements, it will lead to a great deviation in the analysis data. If you are not familiar with the requirements for the use of standard gas, you will not be able to obtain correct data results, which will cause trouble to air separation production.

　　A qualified analytical engineer needs to constantly learn and research new analytical instrument technologies and new instrument analysis technologies, and apply them to his or her job in a timely manner to achieve the goal of excellence and improvement of analytical detection technology. An analytical engineer should not only be able to make the best use of existing equipment, but also absorb foreign and domestic advanced analytical technologies at any time based on a deep understanding of the principles, structures and performance of the instruments currently used, continue to innovate in technology, and further improve and improve the detection level of existing instruments, rather than just being satisfied with simple operation.

　　Conclusion

　　In short, trace gas analysis is a specialized technology and a research-based work, which determines the application effect and level of gas analysis instruments. Trace gas analysis technology is also a practical science. It must go through a lot of experimental practice to explore the regularity of the chemical, to master it well, and to satisfactorily solve various specific trace gas analysis topics. This is also the experience summary of the first generation of gas analyzers in my country when they began to develop high-purity gases in the 1960s and 1970s. This conclusion drawn from their decades of gas analysis should attract the attention of future generations. We hope that gas analysis technicians can achieve faster and greater development under the new situation of rapid development of air separation. Shanghai Shuangxu Electronics Co., Ltd. is willing to work with all colleagues to make due efforts for domestically produced gas analyzers and promote their qualitative leap to a higher level.