Primary standard for the calibration of refrigerant leak flow rates
Résumé
Leak detection is widely used nowadays in various fields such as the automotive and refrigeration industries. The leak tightness of installations charged with refrigerants must be controlled periodically by refrigerant gas detectors, qualified by refrigerant leaks called reference leaks or 'calibrated' leaks. To this day, those refrigerant leaks are not traceable to the SI units under their operating conditions. Therefore, a project involving the LNE, the CEP and the ADEME was initiated in order to develop a national standard for calibrating refrigerant reference leaks. The method consists in measuring the accumulation of gas due to the refrigerant leak inside a closed volume at atmospheric pressure. The leak flow rate is deduced from the concentration variation, measured with a photo-acoustic spectrometer, the pressure and temperature in the accumulation volume and the capacity of the accumulation volume. The uncertainty budget thus takes into account the measurement uncertainties of these quantities. The main components of the uncertainty are due to the accumulation volume capacity and the measurement of concentration. The relative expanded uncertainty of leak flow rates between 1 g yr−1 and 50 g yr−1 is around 2%, depending on the value of the leak.