A New Generation of Mercury Manometers at the IMGC

A new family of primary standards for both absolute and relative pressures in the range 1 kPa to 120 kPa has been designed at the IMGC. The standards make use of laser interferometry, with floats supporting cube-corner retroreflectors, to detect the mercury menisci inside a U-tube and measure their vertical displacements. A description of the first apparatus, HG-3, and an evaluation of its measurement uncertainties are given; the overall uncertainty (at the ± 1 σ level) is lower than ± 0,24 Pa at 1 kPa and ± 0,46 Pa at full scale. A second-generation instrument, HG-5, now being constructed, includes several significant improvements, among which are better control and measurement of temperature and a different interferometric configuration.