<div>The acoustic volume measuring method is a promising non-contact method for volume determination of mass weights. To improve the measuring accuracy of volume determination with the non-contact acoustic method, an acoustic measuring system with two measuring chambers is newly designed to compensate for the non-linearity measuring errors. When reducing the remaining air in the measuring chamber, the measuring accuracy can be greatly reduced. The volumes of mass standards ranging from 100 g to 5 kg are tested to evaluate the non-linearity errors of the volume measurement. The relative uncertainties of the acoustic volume determination are below 7.0 ×10^-4 (<em>k</em>=2).</div>

Keywords: Sound pressure distribution, Volume measurement, Finite element method.Abstract. Stable and uniform sound distribution is a key factor in high precise volume determination of solid material especially for mass standards. A numerical study is carried out to study the distribution and uniformity of sound pressure. The FEM simulation results show that the sound pressure distribution gradient of the small chamber is better than large chamber. With the FEM model in this paper, the maximum sound pressure level change is only 0.003 DB (RMS). And also for small chamber, the sound pressure signals are higher and more easily to be acquired for real measuring system.

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Abstract. This paper analyses the influence of air pressure regarding the precise mass measuring process. The stability of air pressure to the mass determination process is discussed experimentally using the new M-one mass comparator. Due to the change of air pressure, air flow and vibration with regard to the weighing hanger can be arisen. The vibration of weighing hanger is from both the base and the air flow. Under air pressure control, the standard deviation of weighing process can be reduced to 0.39 µg.

With the revision of the definition of the kilogram, more and more weights made of non-metal material, such as silicon spheres and PM 2.5 film, need to be determined with high accuracy. As conventional mass is commonly used in mass metrology, this paper discusses the mass-measuring process for silicon and PM 2.5 film. Electrostatic eliminators are used to eliminate the electrostatic effects of non-metal material to improve the stability of mass measurement. Due to the big difference of weights’ densities, the air buoyancy correction and its uncertainty evaluation are also conducted.