Comparison of pressure standards in the range 10 kPa to 140 kPa

The uncertainty budget of the BIPM primary standard manobarometer of the BIPM-Jaeger type, which has been replicated commercially for use in other national metrology laboratories, has been re-assessed. The effect of different media on the paths of the two white-light beams sensing the mercury column height has been studied using the actual spectrum of the light. The dominating contributions to the overall uncertainty have been reduced substantially.

Section: Discussionsupporting

confidence: 70%

Improved measurement accuracy and uncertainty budget of the BIPM primary standard manobarometer

Stöck

Pello

1999

“…The most important metrological use of mercury today is in the realization of the unit of pressure, with mercury manometers using the hydrostatic pressure p of a liquid column of height h: p = gρ Hg h, with g being the gravitational acceleration. Here, not only the high density but also the low vapour pressure of mercury (table 1) are favourable, allowing uncertainties of a few 10 −6 p to be reached [8]. Although problems with temperature stability and with the meniscus due to the extremely high surface tension of mercury usually limit the accuracy [9], there seems to be no physical reason why mercury manometers should not reach relative uncertainties of even less than 1 × 10 −6 , provided the density of the mercury sample is known with such a small relative uncertainty.…”

Section: Introductionmentioning

confidence: 99%

Density of mercury—measurements and reference values

Bettin¹,

Fehlauer²

2004

After a brief overview of the use of the density of mercury in metrological applications, the methods used for absolute and relative density measurements of mercury and the results obtained are reviewed. Influences exerted on the density by temperature, pressure, isotopic composition, and impurities are discussed, and the formulae recommended at present are listed. The problems arising from the use of the recommended substance properties for an unknown mercury sample are discussed.

“…Since mercury manometers are still the most accurate type of pressure standard [4], the density of mercury is of basic importance for the realization of the pressure scale by the hydrostatic pressure, , of mercury. Uncertainties (for a coverage factor ) of 0.1 Pa to 0.4 Pa near 101 kPa are claimed for modern mercury manometers [5], but the last comparison of pressures in the range 10 kPa to 120 kPa organized by the Consultative Committee for Mass and Related Quantities (CCM) revealed discrepancies of up to 3 Pa [5]. Although the densities of most of the mercury samples used were not measured, the discrepancies are probably not caused by density differences [6].…”

Section: Introductionmentioning

confidence: 99%

New apparatus for measuring the density of mercury

Bettin

Krumscheid

1999

A new apparatus is being set up for measuring the density of mercury at 20 C with a relative uncertainty of 0.5 ϫ 10 -6 by hydrostatic weighing of a sinker of known volume and mass. Two small sinkers of about 50 cm 3 were calibrated by hydrostatic comparison with silicon density standards. Thus, in the first stage, a relative uncertainty of 2 ϫ 10 -6 of the mercury density can be reached. The quantity of mercury needed for the measurements is 1 l. Also, density comparisons of different mercury samples can be carried out with a relative uncertainty of 0.5 ϫ 10 -6 . To reach a relative uncertainty of 0.5 ϫ 10 -6 in the density of mercury, a 500 cm 3 hollow cube is to be manufactured from tantalum. Its volume will be determined by means of an interferometer, with a relative uncertainty of 0.15 ϫ 10 -6 . Measurements will be performed for the gravitation experiment of Zürich University using 1 m 3 of mercury, and for mercury samples used in primary pressure standards. Design and results of first tests of the hydrostatic weighing apparatus are reported.