Automated Mass System for the Avogadro Project

摘要

The Atomic Kilogram Project (also known as the Avogadro Project) aims to redefine the kilogram by linking the molar volume to atomic volume of atoms in a single crystal silicon sphere. Molar volume is molar mass divided by density and measurement of the mass and volume of the sphere is required to determine density. NMIA has developed a fully automated system to determine the mass of silicon spheres which improves the measurement by reducing operator influences and also allows for results to be gathered and processed quickly and efficiently. Two of the main sources of error when prolonged weighing of an object in air is attempted are the effect of air buoyancy and possible convection currents due to temperature gradients caused by heat sources such as the body of the operator. An automated system can assist greatly by reducing these effects with measurements conducted over extended periods, without an operator, particularly during non-working hours when conditions are often most stable. Automation of the weighing process necessitated the design and construction of a precision mechanical loading system with appropriate control and measurement software. Labview software has been designed to control and monitor parameters such as balance readings and environmental conditions and record these at regular intervals for later examination. An analysis program has been developed to process the large amounts of data collected, perform the calculations and produce a final report. This program also graphically represents measured and calculated quantities allowing for the sensitivity of the final result to its input parameters to be viewed, understood and quantified.