Intercomparison of stainless steel kilogram standards

Final Report

The comparison was completed and published in the KCDB.

Project Description

The majority of national standards laboratories maintain mass scales which are based on Pt-Ir copies of the International Prototype Kilogram calibrated by BIPM. For practical purposes mass standards of stainless steel (or alloys of similar density) are used for the dissemination of the mass scale. It is therefore necessary to compare kilogram standards of very different densities at the initial stages of the dissemination process. This introduces a number of sources of uncertainty due to their differences in volume, surface area, etc, and air buoyancy and the measurement of air density make a more significant contribution.

The aim of this project is to intercompare the stainless steel kilogram mass standards of the participating laboratories by checking the compatibility of measured mass values through the calibration of a transfer standard. This will also indicate whether the estimates of the type B uncertainties require re-examination.

The transfer standards will be carefully selected and monitored by the pilot laboratory (NPL) before being measured by each of the participant laboratories. The transfer standards will be hand carried between laboratories and their mass will be monitored at regular intervals by the pilot laboratory. The comparison data will be analysed by IMGC. The intercomparison work will start after participants have recalibrated their standards after completion of the Third Verification of Pt-Ir kilograms at BIPM.

Further Information

This project will run in parallel with a similiar worldwide intercomparison organised by the Working Group for Mass of the CCM, in which BIPM will act as pilot laboratory