气体分析. 采用动态法制备校准混合气体. 第2部分: 活塞泵

[中文适用范围]： 校准气体混合物的制备。 ISO 6145 的这一部分描述了使用活塞泵的方法和制备系统。 混合物成分及其相关的不确定性基于通过尺寸测量对活塞泵进行校准。 使用此方法制备的校准气体混合物由两种或多种成分组成，使用气体混合泵由纯气体或其他气体混合物制备。 这种气体混合泵包含至少两个活塞泵，每个活塞泵以规定的冲程比驱动，以及用于气体供给和混合物均质化的适当附件。 ISO 6145 的这一部分仅适用于包括腐蚀性气体在内的气态或完全汽化组分的混合物，只要这些组分既不相互反应也不与混合泵的润湿表面发生反应。 还涵盖了使用气体混合物作为母体气体。 多组分气体混合物和多步稀释程序包含在本国际标准中，因为它们被认为是双组分混合物制备的特殊情况。 ISO 6145 的这一部分描述了一种制备校准气体混合物的方法，其成分以体积分数表示。 附录 A 中给出了用物质含量分数表示气体成分所需的方程和相关的不确定性评估。 采用这种方法，只要采取足够的质量保证和控制措施，就可以用相对扩展的范围来制备校准气体混合物。 体积分数的不确定性为 0.5 %（覆盖系数 k = 2）。 附件 B 至 D 中给出了数值示例，表明在特定条件下可以获得更小的不确定性。 使用这种方法，可以以离散增量实现 1:10000 的稀释比。 较低的分数（低至 1 × 10−8）可以通过多级稀释或使用气体混合物作为输入气体来实现。 根据所使用的设备，最终混合物流速可以达到 5 l/h 至 500 l/h。 [外文原描述]： ISO 6145 comprises a series of International Standards dealing with various dynamic methods used for the preparation of calibration gas mixtures. ISO 6145-2:2014 describes a method and preparation system using piston pumps. The mixture composition and its associated uncertainty are based on calibration of the piston pumps by dimensional measurements. The calibration gas mixtures prepared using this method consist of two or more components, prepared from pure gases or other gas mixtures using gas-mixing pumps. Such gas-mixing pumps contain at least two piston pumps, each driven with a defined ratio of strokes, and appropriate accessories for gas feeding and mixture homogenization. ISO 6145-2:2014 is applicable only to mixtures of gaseous or totally vaporized components including corrosive gases, as long as these components neither react with each other nor with the wetted surfaces of the mixing pump. The use of gas mixtures as parent gases is covered as well. Multi-component gas mixtures and multi-step dilution procedures are included in this International Standard as they are considered to be special cases of the preparation of two-component mixtures. ISO 6145-2:2014 describes a method of preparing calibration gas mixtures whose composition is expressed in volume fractions. The necessary equations and associated uncertainty evaluation to express the gas composition in amount?of?substance fractions are given in Annex A. With this method, provided that sufficient quality assurance and control measures are taken, calibration gas mixtures can be prepared with a relative expanded uncertainty of 0,5 % (coverage factor k = 2) in the volume fraction. Numerical examples showing that under specified conditions smaller uncertainties are attainable are given in Annexes B through D. Using this method, dilution ratios of 1:10 000 can be achieved in discrete increments. Lower fractions (down to 1 × 10−8) can be achieved by multi-stage dilution or by the use of gas mixtures as input gases. Final mixture flow rates of 5 l/h to 500 l/h can be realized depending on the equipment used.