Measurements of the Compressibility of Working Liquid of a Laser Interferometric Oil Manometer with the Help of a Low-Pressure Interferometric Piezometer

We developed a low-pressure interferometric liquid piezometer aimed at the determination of correction to the density of the working liquid of a laser interferometric oil manometer used as a component of the GET 101–2011 State Primary Pressure Standard for the range of absolute pressure 0.1–7·10⁵ Pa. The indicated correction is caused by the compressibility of the working liquid. The comparison of the obtained correction with changes in the density of the working liquid as a result of its deep degassing (measured at the Physical Technical Institute, Germany) shows that, under the working conditions of the laser interferometric oil manometer, these two effects compensate each other almost completely. This confirms the reliability of the results of pressure measurements within the range 0.1–10³ Pa performed by using the GET 101–2011.