Comparison of the calibrations of high resolution hydrometers for liquid density determinations
Project Description
New European metrological realities and an increasing of precise and traceable measurements of liquid density have been presented since the previous comparison carried out in 1993-94 (EUROMET Project 236). A new comparison on the calibration of high resolution hydrometers will be carried out amongst NMI labs. To harmonise different calibration levels. The comparison is intended to be a regional KC according to the MRA. It should provide support provisional entries to the CMC tables in this subfield. The participant labs will be divided into two groups and will be free to perform measurement of this comparison using their own procedure.
Final Report 2007-09-27
The comparison has been completed and the results are available in the KCDB.
The main objective of the project was to determine the extent of comparability among participating NMIs in performing calibrations of high-resolution hydrometers for liquid density determination in the range between 600 kg/m3 and 1300 kg/m3. After some unforeseen difficulties relating to artefact breakage, transportation, customs and administrative constraints, the project went on two independent petals in the density ranges of 600 kg/m3, 800 kg/m3 and 1 000 kg/m3, and on a single one in the density range 1 300 kg/m3.
As pilot laboratory, INRIM collected all results from all laboratories and determined a single KCRV for each petal.
With the aim of including the contribution of all participating NMIs, the pilot laboratory calculated the KCRV using either the weighted mean, or a more robust one, such as the median, as estimator. This was suggested in case some of the institutes’ measurements appeared to be anomalous or discrepant and a consistency check failed.
The EUROMET project 702 (EUROMET.M.D-K4) was not only useful to each participant to determine their degrees of equivalence with the key comparison reference value, but also to gain more knowledge of their own capabilities in the calibration activities and in measuring the liquid density. Some systematic differences and either underestimated or overestimated uncertainties can be identified between the submitted results, although a particular good agreement was found among the results provided by most of the participants. Last but not least the results allowed also to determine the degree of equivalence between pairs of the participating NMIs.
In conclusion, these results could support the reduction of some uncertainty contributions of some participants, the degrees of equivalence in this comparison will serve as a basis for the new Calibration Measurement Capabilities (CMC) entries on hydrometer calibration and, finally, the experience acquired in this key comparison shall be taken into account in conducting the planed CIPM key comparisons and further intercomparisons in the future.