标准编号：ISO 6145-7:2018
中文名称：气体分析 动态容量法制备校准混合气体 第7部分：热质流控制器
英文名称：Gas analysis — Preparation of calibration gas mixtures using dynamic methods — Part 7: Thermal mass-flow controllers
发布日期：2018-12
标准范围
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.
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