ISO 6142-1:2015 pdf free

ISO 6142-1:2015 pdf free.Gas analysis一Preparation of calibration gas mixtures
The mass of each component is determined by weighing either the supply cylinder, or the cylinder in which the calibration gas mixture will be contained, before and after each addition. The difference in these two weighings corresponds to the mass of the component added. The choice between these two weighing procedures depends on the uncertainty required for the amount fraction of the final mixture. Annex A provides more guidance on precautions to be taken when weighing, handling, and flling cylinders.
NOTE In the case of an addition of a small mass of a specified component, a highly sensitive balance is needed.If such a balance has insufficient capacity to weigh the final mixture, a small added mass can best be determined by weighing a low-volume supply cylinder before and after addition of the component to the main cylinder. A single-step preparation method may be used when the mass of each component added is large enough to be measured accurately. Alternatively, a multiple-step dilution method may be used to obtain a final mixture with acceptable uncertainty, particularly when low amount fractions are required. In this method, “pre-mixtures” are prepared gravimetrically and used as parent gases in one or more of the steps.
An example of the steps used to prepare a calibration gas mixture is given in Annex B.
The determination of the purity of each material (liquid or gas) used in the preparation of the mixture is described in Clause 7. Clause 8 describes the determination of masses and the calculation of preparation uncertainty. The homogeneity and stability of the gas mixture are dealt with in Clause 9.
The verification of the amount fraction of the components in the final mixture against independent standards is described in Clause 10. The calculation of the uncertainty of the calibration gas mixture is given in Clause 11.
The gravimetric method scheme for preparing calibration gas mixtures, based on requirements for composition and the level of uncertainty, is given as a flowchart in Figure 1. The individual steps are explained in more detail in the following clauses (reference is given to the subclause for each step in Figure 1).ISO 6142-1 pdf download.