DIN EN ISO 6145-7:2011-03

This document (EN ISO 6145-7:2010) contains the German translation of the International Standard ISO 6145-7, which has been prepared by Technical Committee ISO/TC 158 "Analysis of gases" (secretariat: NEN, Netherlands). The responsible national Committee is Working Committee NA 062-05-73 AA "Gasanalyse und Gasbeschaffenheit" ("Gas analysis and gas quality") of the Materials Testing Standards Committee (NMP).
This part of ISO 6145 is one of a series of International Standards dealing with various dynamic volumetric methods used for the preparation of calibration gas mixtures. This part specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by use of commercially available thermal mass-flow controllers.
If this method is employed for the preparation of calibration gas mixtures, the optimum performance is as follows: the relative expanded uncertainty of measurement, U, obtained by multiplying the combined standard uncertainty by a coverage factor k = 2, is not greater than 2 %.
If pre-mixed gases are used instead of pure gases, mole fractions below 10^-6 can be obtained. The measurement of mass flow is not absolute and the flow controller requires independent calibration.
The merits of this method are that a large quantity of the gas mixture can be prepared on a continuous basis and that multicomponent mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized.