A Primary Dead-Weight Tester for Pressures (0.05-1.0) MPa

Area of Science:

• Metrology
• Pressure Measurement
• Mechanical Engineering

Background:

• Technological progress in fabricating large-diameter pistons and cylinders with precise geometry.
• Enhanced capabilities in accurately measuring component dimensions.
• Previous limitations in pressure generation uncertainties compared to manometers.

Purpose of the Study:

• To describe a new 35 mm diameter piston/cylinder assembly (PG-39) for pressure standardization at NIST.
• To evaluate the dimensional accuracy and geometric properties of the piston and cylinder artifacts.
• To estimate the relative uncertainties associated with the effective area of the assembly.

Main Methods:

• Utilized a 35 mm diameter piston/cylinder assembly (PG-39) as a pressure standard.
• Accurate dimensioning of both piston and cylinder by Physikalisch Technische Bundesanstalt (PTB).
• Geometric assessment of roundness (within ±30 nm) and straightness (within ±100 nm).

Main Results:

• Piston and cylinder exhibited excellent roundness and straightness over a significant portion of their heights.
• PTB provided precise diameter measurements at 20 °C with an uncertainty of ±15 nm.
• Estimated relative uncertainties for the effective area were approximately 2.2 × 10⁻⁶ (1σ).

Conclusions:

• The PG-39 assembly, due to its precise fabrication and accurate dimensioning, serves as a reliable pressure standard.
• The achieved uncertainties approach those previously attainable only by manometers.
• Advances in metrology enable dead-weight testers to provide highly accurate pressure generation.