EN ISO 6145-4:2008

1 Scope
2 Normative references
3 Principle
4 Application to preparation of gas mixtures
  4.1 Description of the experimental procedure
  4.2 Area of validity
  4.3 Operating conditions
5 Expression of results
  5.1 Volume fraction
  5.2 Sources of uncertainty
  5.3 Uncertainty of volume fraction
Annex A (informative) Pre-mixed gases for preparation of
                      mixtures of high dilution
Annex B (informative) Example of apparatus for preparation
                      of calibration gas mixtures
Annex C (informative) Practical hints
Annex D (informative) Example of the determination of the
                      uncertainty in the concentration of a
                      calibration gas mixture prepared by the
                      continuous injection method
Bibliography

ISO 6145-4:2004 specifies a method for continuous production of calibration gas mixtures, containing two or more components, from pure gases or other gas mixtures by continuous injection of the calibration component(s) into a complementary gas stream by means of a syringe.If pre-mixed gases are used instead of pure gases (see Annex A), much lower volume fractions can be obtained. The volume flow rates, from which the volume fractions are determined, can be calculated from the individual flow rates and can be independently measured by a suitable method given in ISO 6145-1.The merits of the method are that a substantial quantity of the gas mixture can be prepared on a continuous basis and that multi-component mixtures can be prepared almost as readily as binary mixtures if the appropriate number of syringes is utilized, or if the syringe already contains a multi-component mixture of known composition. This method also provides a convenient means for increasing the volume fraction of the calibration component in the mixture in small steps. It is therefore a useful method for evaluation of other characteristics of gas analysers, such as minimum detection limit and dead zone, as well as accuracy. The relative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) is 5 % and the range of applicability is 10-5 to 10-2.