Primary Gas Pressure Standard Passes Next Stress Test

Abstract

AbstractIn 2020, Nature Physics 16, 177 (2020) presented a primary gas‐pressure standard, based on temperature and electrical measurements and ab initio calculations of the thermophysical properties of helium. It is compared against the world's most accurate primary mechanical pressure standard and the test is successful with a relative uncertainty of 5 parts per million (ppm) at about 7 MPa. This is feasible for two reasons. First, the experimental setup developed for the determination of the Boltzmann constant is capable of achieving a combined relative uncertainty on the level of 2 ppm and the primary mechanical pressure standard 1 ppm. The latter consists of two pressure balances with five piston‐cylinder assemblies. Second, the uncertainties of the theoretical calculations in 2020 are on the level of about 4 ppm. Within the last two years, significant improvement has been achieved for all theoretical quantities involved, and the uncertainty contribution of the theory is below the level of 1 ppm. With doubled sensitivity, the thermodynamic gas‐pressure standard is compared to the most accurate mechanical pressure standard. This stress test for theory and experiment is once again successful.