Final report of key comparison CCM.P-K12 for very low helium flow rates (leak rates)

Abstract

Quantitative leak tests with vacuum technology have become an important tool in industry for safety and operational reasons and to meet environmental regulations. In the absence of a relevant key comparison, so far, there are no calibration measurement capabilities published in the BIPM data base. To enable national metrology institutes providing service for leak rate calibrations to apply for these entries in the data base and to ensure international equivalence in this field, key comparison CCM.P-K12 was organized. The goal of this comparison was to compare the national calibration standards and procedures for helium leak rates. Two helium permeation leak elements of 4×10−11 mol/s (L1) and 8×10−14 mol/s (L2) served as transfer standards and were measured by 11 national metrology institutes for L1 and 6 national metrology institutes for L2. Equivalence could be shown for 8 laboratories in the case of L1 and for all 6 in the case of L2. Three different evaluation methods were applied and are presented in this report, but the random effects model was accepted as most suitable in our case.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Gas flow standards and their uncertainty

“…The results of comparisons are collected in reports that can be found in the Key Comparison Database (https://bipm.org/kcdb/). The most relevant comparison reports are [12][13][14][15][16][17] in which many of the piston provers, bell provers, PVTt, rate of rise, gravimetric, and working flow standards used as examples herein have successfully validated their uncertainty claims.…”

Volume calibration using a comparison method with a transfer leak flow rate

“…Replacing the throughput (equation (1)) by the molar flow rate [4], we obtain for a constant gas temperature :…”

Characterization of spinning rotor gauge-3 using orific flow system and static expansion system

“…The working principle of the OFS is based on the flow of gas in molecular flow regions through the orifice of known conductance (C) connected across two chambers [10]. If Q is the flow rate of the gas throughout then the pressure upstream is given by equation (2) = (1 + ) ,…”

“…Among these standards, this section has two primary vacuum standards OFS and SES which measure the pressure in the range of 0.1 Pa to 1 µPa and 0.05 Pa to 10 Pa, respectively with associate uncertainty 2% and 0.4% of the pressure reading at k=2. The vacuum primary standards have participated in the international key comparisons [1,2] and found the reputations at the global level. There are many other transfer standards like resonant silicon gauge (RSG), old spinning rotor gauge (SRG 2), capacitance diaphragm gauge (CDGs), etc.…”