Buoyancy effects and correlations in calibration and use of electronic balances

A regular assessment is fundamental to ensure that a balance provides reliable and accurate weighing results. Calibration is the main means to establish the relation between the balance indications and the reference standards, which will be applied in the use of the balance in order to obtain a traceable result. The main problem in the calibration of high-resolution balances is related to the corrections of the buoyancy effects. In addition, electronic balances can be compensated, for their drift due to changes in temperature, air density and other influence factors, by the adjustment function. This paper analyses in detail the influence of these effects on the weighing and proposes an original model to be used in the calibration and in the subsequent use of the balance. The uncertainty evaluation has been studied with the aim to separate the uncertainty due to the calibration process from that of the balance in use, taking also into account the correlations between the input estimates. This analysis has revealed important aspects on the uncertainty of the weighing result to be considered in high-resolution balances.