The gas generators for calibration based on the use of “Method of Permeation Tubes.”
The permeation tubes are sealed capsules containing a small amount of the component that is in contact with a permeable membrane stable. The permeation through the membrane produces a vapor of the compound of the component of small quantity, very stable as a stream in time. This permeate stream by mixing with a dilution gas controlled and precise (for example nitrogen) creates a mixture in track at the desired concentration. The flow of the permeate is measured metrically through severe weight loss of the tube thus ensuring a standard high precision.