To overcome the influence of liquid surface tension on the density measurement of single-crystal silicon sphere with hydrostatic method, pressure-of-flotation (PF) method and measurement system were developed to carry out the comparison measurement of single-crystal silicon sphere density. On the condition of certain temperature, the pressure of liquid was adjusted, which caused the change of liquid density, and the standard and measured single-crystal silicon spheres could be suspended in the liquid stably. By measuring liquid temperature, pressure and suspension heights, the density difference was determined. Double - level temperature control system was used to achieve stable temperature within ±0.25 mK. The liquid compress coefficient was determined by the linear equation of temperature - pressure suspension condition. It was verified by experiments that the density difference of single-crystal silicon spheres could be measured with high precision, and the standard relative uncertainty is 2 × 10-7 .%为了克服单晶硅球密度测量静力称重法精度受液体表面张力的影响,研究了压浮法进行单晶硅球密度精密比较测量方法和测量系统.在一定的温度下,调节压力,利用液体压缩系数控制液体密度使标准单晶硅球和被测单晶硅球稳定悬浮于工作液体中,通过温度、压力和悬浮高度的测量,计算出二者之间的密度差值.通过双层控温系统保证了液体温度长期波动在±0.25 mK内,利用标准单晶硅球在不同温度-压力悬浮条件线性关系计算出液体压缩系数.试验证明,压浮法测量装置实现了单晶硅球密度差值的精密测量,标准测量相对不确定度为2×10-7.
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