Mettler-Toledo M_one vacuum mass comparator

The Mettler-Toledo M_one is a suitable reference instrument for mass comparison under a controlled environment. The product is said to minimise all sources of uncertainty from the environment, the process and even itself during both measurement and transport, making it vital in the race to define the kilogram based on physical constants. It delivers results accurate to 0.1 µg with typical repeatability of 0.3 µg.

The race to redefine the kilogram involves two experiments: one using a Watt balance and the other using the Avogadro principle. To share and disseminate the investigated artefacts, each artefact must be transferred in a contamination-free atmosphere. Eliminating human error through automation, the M_one vacuum pumping system enables the necessary controlled environment starting at ambient pressure and going down to a vacuum level of 10^-6 mbar.

Ergonomic design allows users to place weights directly onto the product’s turntable through a large, quick-loading door. The system is sealed and allowed to reach desired atmospheric conditions. Once this pressurised environment is reached, the artefact is never exposed to air again. An Artefact Storage and Transport Vessel (ASTV), Artefact Transfer Device (ATD) and automatic Load Lock arm facilitate easy transfer of the artefact and preserve the pressure required to deliver necessary stability.

Once the artefact reaches the measurement chamber during comparisons, it is placed on a star-shaped weighing pan designed to accept various artefact shapes, such as cylindrical weights and silicon spheres from 100 g to 1 kg without adapter plates. Automated gravimetric centring (AGC) ensures correct positioning, minimising eccentricity and ensuring high repeatability.