Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 1: General aspects
1 Scope
This document gives a brief overview of each of the dynamic techniques which are described in detail the subsequent parts of lS0 6145. This document provides basic information to support an informed choice for one or another method for the preparation of calibration gas mixtures, It also describes how these methods can be linked to national measurement standards to establish metrological traceability for the composition of the prepared gas mixtures. Since all techniques are dynamic and rely on flow rates, this document describes the calibration process by measurement of each individual flow rate generated by the device. Methods are also provided for assessing the composition of the generated gas mixtures by comparison with an already validated calibration gas mixture. This document provides general requirements for the use and operation of dynamic methods for gas mixture preparation, It also includes the necessary expressions for calculating the calibration gas composition and its associated uncertainty.
Gas mixtures obtained by these dynamic methods can be used to calibrate or control gas analysers. The storage of dynamically prepared gas mixtures into bags or cylinders is beyond the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document, For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6143 Gas analysis - Comparison methods for determining and checking the composition of calibration gas mixtures
Note: GB/T 10628-2008, Gas analysis - Comparison methods for determining and checking the composition of calibration gas mixtures (ISO 6143:2001, IDT)
ISO 7504 Gas analysis-Vocabulary
Note: GB/T 14850-2020, Gas analysis-Vocabulary (ISO 7504:2015, IDT)
ISO 12963 Gas analysis - Comparison methods tor determination of the composition of gas mixtures based on one-and-two-point calibration
ISO 14912 Gas analysis - Conversion of gas mixture composition data
Note: GB/T 40870-2021, Gas analysis - Conversion of gas mixture composition data (ISO 14912:2003, IDT)
ISO 19229 Gas analysis - Purity analysis and the treatment of purity data
Note: GB/T 38521-2020, Gas analysis - Purity analysis and the treatment of purity data (ISO 19229:2015, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IS0 7504 and the following apply.
3.1
mass flow rate
qm
mass of gas per unit of time
3.2
volume flow rate
volume of gas per unit of time
qv
4 Symbols
For the purposes of this document, the following symbols applies.
5 Principle
5.1 General
All preparation techniques described in ISO 6145 (all parts) are based on the combination of gas flows. These flow rates can be measured on a volume or mass basis, The composition is calculated from the flow rate data and the composition of the parent gases.
It is applicable only to
——pure gases,
——gas mixtures, or
——totally vaporized components at ambient pressure,
which do not react with each other or with any surfaces of the mixing device.
