EN ISO 6145-8:2008

Foreword
Introduction
1 Scope
2 Normative references
3 Principle
4 Reagents and materials
5 Apparatus
6 Procedure
  6.1 Preliminary checks and operating conditions
  6.2 Determination of mass loss
7 Expression of results
  7.1 Calculation
  7.2 Sources of uncertainty
Annex A (informative) Practical example of a diffusion cell
                      calibrator configured for evaluating
                      speed of response in a hygrometer
Annex B (informative) Example of performances of diffusion
                      cells for toluene and trichloromethane
Annex C (informative) Example of uncertainty calculations for
                      a periodic weighing system
Bibliography

ISO 6145-8:2005 specifies a dynamic method using diffusion for the preparation of calibration gas mixtures containing component mole fractions ranging from 10-9 to 10-3. A relative expanded uncertainty of measurement, U, obtained by multiplying the relative combined standard uncertainty by a coverage factor k = 2, of not greater than ± 2 % can be achieved by using this method.By keeping the path between the diffusion source and place of use as short as possible, the method can be applied for the generation of low-concentration calibration gases of organic components that are liquid at room temperature, with boiling points ranging from about 40 °C to 160 °C. ISO 6145-8:2005 is applicable not only for the generation of calibration gas mixtures of a wide range of hydrocarbons at ambient and indoor air concentration levels, but also for the generation of low-concentration gas mixtures of water.