Abstract: The working principle of density-type gas purity on-line detection device based on the centrifugal fan impeller theory was introduced, and the influence of mixed gas composition on its measuring error was analyzed. The factors, which influence on the measuring accuracy caused by improper operation and maintenance, were summarized, and the method for preliminary determination of the detector measuring accuracy was given also.

Key words: gas purity, principle of detection, steam turbo-generator, error analysis