Perspectives of atmospheric reference leaks calibration by gravimetric method

The measurement of freon (mainly R134a) leaks is an important task of metrology. The paper deals with the study of the possibilities of improvement of gravimetric traceability method for the permeation secondary standards of atmospheric freon leaks. Their leak rates are different under atmospheric and vacuum conditions; only the first one is interesting for practical use. Moreover, the desirable steady state after changing the conditions is achieved only after certain relaxation time. This complicates the correction of the buoyancy influence, which causes the uncertainty increase. The leak rates of a typical secondary standard of this kind under atmospheric and vacuum conditions are compared, the needed relaxation times searched and some possibilities of further improvement discussed.

► A gravimetric primary standard of freon leaks was developed and tested.
► A problem of the buoyancy influence was being solved.
► A gravimetric method performed in a hermetically closed vessel is very promising.