Primary pressure standards based on dimensionally characterized piston/cylinder assemblies

Abstract

NIST has characterized two large diameter (35.8 mm) piston/cylinder assemblies as primary pressure standards in the range 0.05 MPa to 1.0 MPa with uncertainties approaching the best mercury manometers. The realizations of the artefacts as primary standards are based on the dimensional characterization of the piston and cylinder, and models of the normal and shear forces on the base and flanks of the piston. We have studied two piston/cylinder assemblies, known at the National Institute of Standards and Technology (NIST) as PG 38 and PG 39, using these methods. The piston and cylinder of both assemblies were accurately dimensioned by Physikalisch Technische Bundesanstalt (PTB). All artefacts appeared to be round within ±30 nm and straight within ±100 nm over a substantial fraction of their heights. PG 39 was dimensioned a second time by PTB, three years after the initial measurement, and showed no significant change in dimensions or effective area. Comparisons of the effective area of PG 38 and PG 39 from dimensional measurements, against those obtained with calibration against the NIST ultrasonic interferometer manometer (UIM), are in agreement within the combined standard (k = 1) uncertainty of the dimensional measurements and the UIM. A cross-float comparison of PG 38 versus PG 39 also agreed with the dimensional characterization within their combined standard uncertainties and with the UIM calibrations. The expanded (k = 2) relative uncertainty of the effective area is about 6.0 × 10 −6 for both assemblies.

Cell-based refractometer for pascal realization

“…We note that the temperature difference between the triple-cell and reference junction was usually within 1 mK at steady state, but a 367 kPa helium fill increased glass temperature by about 45 mK, and we had to wait 4 h for the transient to settle before measuring refractivity; this process is the main driver behind our requirement on MIRE stability. We used a piston gauge to generate a known gas pressure, which had been previously compared to a primary pressure standard [20], and thus our uncertainty is a combination of the primary standard and cross-float comparison uncertainties. Last is the uncertainty due to gas impurity: we are limited by the 99.9999% purity helium that comes from standard cylinders and analysis certificates; we envisage that a next-iteration MIRE, having triple-cells made in low-thermal-expansion glass ceramic and with smaller d w would need to purify through a liquid-helium cold-trap.…”

Polarizability of Helium and Gas Metrology

“…The pressures p lab were measured with a pressure balance (piston and cylinder) that had been calibrated by comparison with one of NIST's primary pressure standards [17]. At low pressures, u r p lab was dominated by the 4.3 ppm uncertainty of the effective area of the piston near 100 kPa.…”

Development of a new high-stability transfer standard based on resonant silicon gauges for the range 100 Pa to 130 kPa

“…The long-term stability of the transfer standard package was evaluated using equation (8) with the results shown in figure 5. Also shown in the plot are the relative uncertainties due to systematic effects for the NIST UIMs [1][2][3][4][5][6][7][8]. This plot shows that the long-term stability of the transfer standard package will enable an excellent comparison of primary standards.…”