We consider the feasibility of basing a pressure standard on measurements of the dielectric constant [epsilon] and the thermodynamic temperature T of helium near )[degrees]C. The pressure P of the helium would be calculated using the fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressure ur(P) would exceed 20x10-6, the relative uncertainty of the value of the molar polarizability of helium A[epsilon] calculated ab initio. If the relativistic corrections to Ad[epsilon] were calculated as accurately the classical value is now known, a capacitance-based pressure standard might attain ur(P)-6 for pressures near 1 Mpa, a result of considerable interest for pressure metrology. One obtains P by eliminating the density from the virial expansions for P and [epsilon]-1. If [epsilon]-1 were measured with a very stable, 0.5 pF toroidal cross capacitor, the small capacitance and the small values of [epsilon]-1 require state-of-the-art capacitance measurements.
Journal of Research (NIST JRES) -
ab initio calculations, cross capacitor, dielectric constant, helium, molar polarizability, polarizability, pressure standard, toroidal cross capacitor