标准摘要
[中文适用范围]： 茂盖料敨接地使用 瑝瘔耗人尢笝比煤扩耯控制朼控性。 [外文原描述]： 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.
英文名称Gas analysis — Preparation of calibration gas mixtures using dynamic methods — Part 7: Thermal mass-flow controllers