Hydrometers are widely used in industry for liquid density measurement. It is important to achieve rapid and high accuracy calibration for hydrometers. Based on the Archimedes principle, a fully automatic hydrometer calibration system in NIM was designed using Cuckow’s method. The liquid density of n-tridecane (C₁₃H₂₈)is calibrated with 441 g high-purity fused silica ring as the solid density standard. The buoyancy of hydrometer is measured by static weighing system with resolution 0.01 mg. The alignment between liquid surface and hydrometer scale was achieved by the lifting platform with the positioning accuracy of 10 μm. According to the weighing value of hydrometer in air and liquid, the density correction value at different scales is calculated. Hydrometer covering a full range (650–1500) kg/m³can be calibrated without changing the liquid. Taking the calibration data of PTB as reference, the experimental data show that the measurement uncertainty of this system is better than 0.3 division (k = 2).

比重计在工业中广泛用于液体密度测量。实现比重计的快速和高精度校准非常重要。基于阿基米德原理，利用Cuckow的方法设计了一个全自动的NIM比重计校准系统。的液体密度Ñ十三烷（C ₁₃ H ^ ₂₈) 使用 441 g 高纯度熔融石英环作为固体密度标准进行校准。比重计的浮力采用静态称重系统测量，分辨率为 0.01 mg。通过升降平台实现液面与比重计刻度的对准，定位精度为10 μm。根据比重计在空气和液体中的称重值，计算出不同刻度下的密度修正值。覆盖全量程 (650–1500) kg/m ^{3 的}比重计无需更换液体即可校准。以PTB的标定数据为参考，实验数据表明该系统的测量不确定度优于0.3div( k  =2)。