The standard applies to the preparation of calibration gas mixtures of various compounds in a diluent gas, with concentrations of 50 - 2000 Mg/m3. The determining factor here is the extent to which the delivery from the permeation tube and the flow rate of the diluent gas can be varied. The release of the permeation tube is strongly dependent on the temperature. E.g. for NO2 the change in release is approximately 10% per degree change in temperature. The temperature of the permeation tube can therefore be used as a setting option for the release of the permeation tube. Replacing the permeation tube with one or more units with a different diffusion surface is also possible. The diluent gas flow rate can be varied by changing the inlet pressure at the critical orifice (0.2 - 0.6 MPa). Critical openings with a different opening can also be used (0.15 - 0.80 mm). This allows flow rates of 0.01 - 2 m3/h to be achieved. By choosing the permeation tube (size of diffusion surface), temperature, critical opening and pre-pressure it is possible to vary the concentration of the calibration gas mixture at least over the range of 50 - 2000 fig/m3. The scope of the standard is limited to calibration gas mixtures containing those compounds that can easily be compressed into liquid (vapour pressure at 20 °C maximum 2 MPa). Examples of these compounds are: acetonitrile, acroleihe, acrylonitrile, benzene, hydrogen cyanide, dicyclopentadiene, methyl mercaptan, vinyl chloride, nitrogen dioxide, styrene, hydrogen fluoride, sulfur dioxide, carbon dis lfide, hydrogen sulfide.
NEN 2042-1982 history
1982NEN 2042-1982 Air quality — Preparation of calibration gas mixtures by means of permeation tubes