In theory, shock tubes provide a pressure change with a very fast rise time and calculable amplitude. This pressure step could provide the basis for the calibration of pressure transducers used in highly dynamic applications. However, conventional metal shock tubes can be expensive, unwieldy and difficult to modify. We describe the development of a 1.4 MPa (maximum pressure) shock tube made from unplasticized polyvinyl chloride pressure tubing which provides a low-cost, light and easily modifiable basis for establishing a method for determining the dynamic characteristics of pressure sensors.

Platinum–iridium (Pt/Ir) kilogram mass prototypes are known to gain contamination from the environment in which they are stored. The current method of cleaning these mass prototypes is called nettoyage–lavage and involves the physical rubbing of a kilogram with a chamois leather cloth soaked in a solvent followed by removal of any solvent residue using a jet of steam water. The manual nature of the technique means the effectiveness of the cleaning process is reliant on the human operative. An alternative cleaning method involving exposure to ultraviolet light and ozone (UV/O3) has been tested on Pt/Ir foils and kilogram mass prototypes. The changes to the surface of the Pt/Ir foils as a result of this process have been quantified using x-ray photoelectron spectroscopy and have shown a clear reduction in the quantity of carbonaceous contamination. Variation of the UV intensity, ozone concentration and exposure duration enabled the optimum cleaning conditions to be established. The UV/O3 cleaning method was then used to clean two Pt/Ir kilogram mass prototypes and gravimetric weighing of the kilograms before and after cleaning gave the amount of contamination removed. These gravimetric weighing results demonstrated that UV/O3 cleaning was as effective as the nettoyage–lavage process.

To determine a new value of the Avogadro constant with a relative combined standard uncertainty of 2 × 10 −8 , the mass determination of a 1 kg 28 Si sphere is crucial and should be determined with the highest level of accuracy. In the next two years the laboratories involved in the International Avogadro Project should be able to determine the mass of a 1 kg silicon sphere under vacuum with a combined standard uncertainty within 5 µg. To obtain such a target it is essential to gain experience and to promote cooperation in mass measurement on silicon spheres among the laboratories involved. For this purpose an international comparison has been performed to evaluate the weighing procedure and to reveal the difficulties encountered in the mass determination of a silicon sphere.This particular comparison, which is the first international mass comparison under vacuum conditions, has demonstrated that the reference value for the mass of a 1 kg silicon sphere can be determined traceable to the International Prototype with a standard uncertainty of 4.0 µg.

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Highly polished spheres, manufactured from silicon single-crystal material, are used in the X-ray crystal density method (XCDM) to determine the Avogadro constant. If the measurement uncertainty associated with this method can be reduced to 0.01 p.p.m., it would be possible to redefine the SI unit of mass, the kilogram, in terms of a fixed number of atoms of a definite species. The spheres are manufactured with a nominal mass of 1 kg and nominal diameter of 90 mm and a surface roughness of 0.5 nm (peak to valley). A goniometer has been constructed to enable the crystallographic orientation of these spheres to be determined using the back-reflection Laue technique. Two spheres have been successfully orientated in this manner by identifying two orthogonal 〈100〉 directions.

This report describes the result of a key comparison of volume standards at twelve European national metrology institutes. This comparison was carried out during the period January 1996 to January 1999 within the framework of the European Collaboration in Measurement Standards (EUROMET) in order to determine the degree of equivalence between the participants for the determination of the volume of solids in the range 87 cm3 to 315 cm3. The pilot institute was the Federal Office of Metrology METAS (former OFMET) of Switzerland. This comparison was initiated and realized before the CCM.D-K1 (Density measurements of a silicon sphere). For that reason no direct link was made between the CCM.D-K1 and the EUROMET.M.D-K1 comparison. The transfer standards consisted of three different spheres made of ceramic material (Si3N4/MgO). The three spheres were calibrated by the participants using hydrostatic weighing either with solid density standard or with water density tables as reference. Stability measurements show that the transfer standards were sufficiently stable during the comparison. The degrees of equivalence of the measurement standards were expressed quantitatively by two terms, deviations from the key comparison reference values and associated uncertainty of measurement for each of the three spheres. Considering all participants, the maximum relative difference between the volume measurements was 1.6 × 10-5 for the biggest sphere (1 kg and 315 cm3). Considering the five participants using a solid density standard as volume reference and having performed automatic mass determination, the maximum relative difference between the volume measurements was 2.2 × 10-6 for the same sphere. This comparison was approved for provisional equivalence of the CMC declared in the field.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 (MRA).