title: Can a Pressure Standard be Based on Capacitance Measurements?
abstract: We consider the feasibility of basing a pressure standard on measurements of the dielectric constantϵand the thermodynamic temperatureTof helium near 0 °C. The pressurepof the helium would be calculated from fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressureur(p) would exceed 20 × 10-6, the relative uncertainty of the value of the molar polarizability of heliumAϵcalculatedab initio. If the relativistic corrections toAϵwere calculated as accurately as the classical value is now known, a capacitance-based pressure standard might attainur(p) < 6 × 10-6for pressures near 1 MPa, a result of considerable interest for pressure metrology. One obtainspby eliminating the density from the virial expansions forpandϵ- 1. Ifϵ- 1 were measured with a very stable, 0.5 pF toroidal cross capacitor, the small capacitance and the small values ofϵ- 1 would require state-of-the-art capacitance measurements to achieve a useful pressure standard.
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Moldover
keywords: ab initio calculations; cross capacitor; dielectric constant; helium; molar polarizability; polarizability; pressure standard; toroidal cross capacitor