Permeation tubes emits the compound with a constant rate and constant temperature, permeation rate have a exponential dependence from the temperature: it increases around 7% for a increase of 1°C. To generate gas standard with accuracy is necessary a thermostation with accuracy ±0,1°C. The tube (or more tubes) are placed into “U” glass older and immersed in thermostatic bath, the diluent air or nitrogen is pre-heated on bed of glass spheres.