When comparing mass standards with large volume differences the density of air is one of the largest uncertainty components for mass. The air density can be determined by direct weighing using buoyancy artefacts or it can be calculated from the CIPM 81/91 formula. A small relative difference (about 6·10^-5) between these two methods exists. The aim of the present work is to verify this difference and to gain experience on vacuum weighing and on the stability of weights. Two buoyancy artefacts with different volumes were utilized. The artefacts were compared in vacuum and in air. From the weighing results air density was calculated and compared with the CIPM formula. The following value for the relative air density difference was obtained 4 x 10^-5 (u=7 x 10^-5).

In the field of calibration, Italy participates to the European framework with SIT(Servizio di Taratura in Italia), which grants accreditation through the verification of the correctness of the calibration of the measurement instruments with reference to the National Standards maintained by the Metrological Institutes INRIM and ENEA.
One of the most important activities of the National Accreditation Body (NAB) is the organisation of a series of interlaboratory comparisons (ILC), at European (EA) and National level, to verify the measurements capability of the accredited laboratories.
In 2004 and In January-February 2005 ILCs, for the calibration of force transducers, were organised in Italy by the SIT with the INRiM (formerly IMGC-CNR and IEN) as pilot laboratory. At the experimental ILCs participated four accredited Calibration Laboratories. The relative deviation up to 20 kN of the calibration machines, from the INRIM standard deadweigh machines (DWM), were allways less than +/- 50 10^–6.

A technique for calibrating force transducers under dynamic input conditions is reported and evaluated. The output of a test transducer is determined at a number of points on an applied input force ramp by comparison with a calibrated reference transducer connected in series, enabling the output sensitivity of the test transducer to be determined. Experimental results show that transducer output values obtained using this dynamic calibration technique are in agreement with those obtained using a static calibration procedure to within 0.05%. This continuous calibration technique provides an alternative to calibrating the transducer statically, greatly reducing the time required for transducer calibration. Investigation of the creep characteristics of a range of test transducers demonstrates that creep performance is a major contribution to agreement between transducers in continuous calibrations, leading to possible techniques for the correction and subsequent improvement of calibration results.

The laboratory of MIKES-Lahti Precision Oy has made over almost twenty years comparisons with the PTB, utilizing more than ten different force transducers. These comparisons have been made regularly every year to supervise the traceability of force. The results of these comparisons are showing different kinds of behaviours. For the traceability the most important characteristic is the stability of the sensitivity. The change of the sensitivity directly influences the measurement uncertainty and as a result affects the final uncertainty of the intercomparison. The second characteristic is the zero reading, which can indicate the change of the measurement behaviour of the transducer.

The present paper describes the preliminary results of the metrological characterization of the newly design and developed force machine to realize the forces in the range 2N- 20N with an expanded uncertainty of 50 ppm. The characterization of the machine is carried out in compression using two transfer force standards of 5 and 20 Newton capacity. The calibration of the transfer standards directly against the dead weight force machine shows that the repeatability and reproducibility are better than 0.002% and 0.003% respectively, over the full range of measurement.