ISO 6145 is a series of documents dealing with various dynamic methods used for the preparation of calibration gas mixtures. This document specifies a method for continuous preparation of calibration gas mixtures@ from nominally pure gases or gas mixtures by use of thermal mass-flow controllers. The method is applicable to preparation of mixtures of non-reacting species@ i.e. those which do not react with any material of construction of the flow path in the thermal mass-flow controller or the ancillary equipment. If this method is employed for preparation of calibration gas mixtures the optimum performance is as follows: the relative expanded measurement uncertainty U@ obtained by multiplying the 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 the method are that a large quantity of the calibration gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared as readily as binary mixtures if the appropriate number of thermal mass-flow controllers is utilized NOTE Gas blending systems@ based upon thermal mass-flow controllers@ and some including the facility of computerization and automatic control@ are commercially available.
EN ISO 6145-7:2018 history
2018EN ISO 6145-7:2018 Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 7: Thermal mass-flow controllers
2010EN ISO 6145-7:2010 Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 7: Thermal mass-flow controllers (ISO 6145-7:2009)