A bilateral comparison of a 1 kg platinum standard

Final Report

Full report

A bilateral comparison on the measurement of mass has been carried out between the national measurement institutes INM, Romania and DFM, Denmark. The purpose of the comparison was to assess the models used by DFM and INM to predict the change in mass of the prototypes over time due to the adsorption of hydrocarbons or other airborne pollutants.

The transfer standard was an old 1 kg platinum standard from 1835 provided by DFM. The standard was first calibrated at DFM by direct comparison with the Danish prototype No. 48. The transfer standard was then carried to INM, where it was compared directly to the Romanian prototype No. 2. Finally, the transfer standard was carried back to DFM, were it was calibrated again. The difference between the two measurements made by DFM was less than 0.001 mg.

The Danish prototype No. 48 was last calibrated (without cleaning) at BIPM in July 2001. Based on the calibration history, DFM has set up a drift model that describes the change in mass (without cleaning) of prototype no 48 since the third verification of the prototypes. The value assigned to no. 48 based on this drift model seems to be consistent with the reference values assigned to two prototypes compared in EUROMET project 509 taking into account the estimated uncertainty (k=1) of 0.005 mg on the results reported by DFM.

The Romanian prototype no. 2 was last calibrated at BIPM during the Third Periodic Verification of National Prototypes of the Kilogram (1988-1992). In order to correct for possible changes in mass since then, INM applied a drift model that took into account the possible change in mass value of the prototype since the verification.

As described in the final report of the comparison[1], the results indicate that the current mass values assigned to the prototypes are slightly inconsistent. As the Danish prototype was recalibrated at BIPM in 2001 and provided consistent results in a similar comparison in EUROMET Project 509 in 2002, it is most likely the drift model assigned to the Romanian prototype that is less accurate than assumed.

[1] Lars Nielsen, A bilateral comparison of a 1 kg platinum standard, DFM Report DFM-03-R60


Proposal

Romania holds the national prototype no. 2, which was last calibrated at BIPM during the Third Periodic Verification of National Prototypes of the Kilogram (1988-1992). The prototype has not been calibrated at BIPM since then, but the laboratory has applied a drift model that takes into account the possible change in mass value of the prototype since the verification.

DFM holds prototype no 48, which was last calibrated (without cleaning) at BIPM in July 2001. Based on the calibration history, DFM has set up a drift model that describes the change in mass (without cleaning) of prototype no 48 since the third verification of the prototypes. The value assigned to no. 48 based on this drift model seems to be consistent with the reference values assigned to two prototypes compared in EUROMET project 509 taking into account the estimated uncertainty (k=1) of 0.005 mg on the results reported by DFM.

The purpose of the bilateral comparison between DFM and INM is to test the consistency of the drift models applied by DFM and INM for the change in mass values of the national prototypes.

Further Information

The comparison is carried out under contract (Ref.: RO0006.05.02) with Deutshe Gesellschaft für Zerstörungsfreie Prüfung (DGZfP) and is funded by the European Community.

Subjects
Mass and Related Quantities (M)
Coordinating Institute
DFM (Denmark)
Participating Partners
INM-RO (Romania)