Mr. Moldover, CAN A PRESSURE STANDARD BE BASED ON CAPACITANCE MEASUREMENTS, Journal of research of the National Institute of Standards and Technology, 103(2), 1998, pp. 167-175
We consider the feasibility of basing a pressure standard on measureme
nts of the dielectric constant epsilon and the thermodynamic temperatu
re T of helium near 0 degrees C. The pressure p of the helium would be
calculated from fundamental constants, quantum mechanics, and statist
ical mechanics. At present, the relative standard uncertainty of the p
ressure u(r)(p) would exceed 20 x 10(-6), the relative uncertainty of
the value of the molar polarizability of helium A(epsilon) calculated
ab initio. If the relativistic corrections to A(epsilon) were calculat
ed as accurately as the classical value is now known, a capacitance-ba
sed pressure standard might attain u(r)(p)< 6 x 10(-6) for pressures n
ear 1 MPa, a result of considerable interest for pressure metrology. O
ne 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 va
lues of epsilon - 1 would require state-of-the-art capacitance measure
ments to achieve a useful pressure standard.