Stability investigations of the transfer and the storage of mass standards in inert gas

The stability of a mass standard determines the intervals at which re-calibration of a standard has to take place and how precisely the results of mass determinations can be compared with each other (e.g. within the scope of international comparison measurements).

The stability of a mass standard determines the intervals at which re-calibration of a standard has to take place and how precisely the results of mass determinations can be compared with each other (e.g. within the scope of international comparison measurements). In preparation of the planned redefinition of the kilogram, part of the task of the European Metrology Research Project EMRP SIB05 NewKILO, which is led by the National Physical Laboratory (NPL, UK), consisted in finding out whether the stability of conventional steel transfer standards was improved by transporting and storing them in protective gas (nitrogen). For this purpose, the participants determined the mass of the transfer standards in vacuum with standard uncertainties (k = 1) between 8 µg and 19 µg. From one participant to the next, the transfer standards were transported and stored in special transport containers filled with nitrogen and others filled with ambient air as usual. The results of the measurements (Figure 1) have shown that transport and storage in protective gas did not lead to an increase in the mass stability [1].

Figure 1: Mass of the transfer standards determined by the participants in vacuum as compared to the initial values measured by the NPL [1]. The mass differences were corrected with respect to essential systematic influences of the traceability of the respective reference standards used to the international prototype of the kilogram. From one participant to the next, the transfer standards were transported and stored in special transport containers filled with nitrogen (blue curve) and others filled with ambient air as usual (red-brownish curve). The uncertainty ranges stated correspond to the standard uncertainties (k = 1).

Literature:

[1] Berry, J. J.; Bentouati, D.; Borys, M.; Högström, R.; Kaçmaz, S.; Malengo, A.; Marti, K.; Mecke, M.; Silvestri, Z.; Snopko, L; Zůda, J.: A comparison between seven National Measurement Institutes to evaluate inert gas transfer of mass standards against current best practice. National Physical Laboratory Report ENG 61 (2015), National Physical Laboratory, Teddington, pp. 1-25

Contact person:

Dr. Michael Borys, FB 1.8, AG 1.81,michael.borys(at)ptb.de