A new instrument for the dimensional characterization of piston-cylinder units

摘要

Calculations of the effective area and elastic distortion of piston-cylinder units (PCUs) used to realize fundamental pressure standards require accurate dimensional measurement of the cylindrical geometry of both the piston and the cylinder. A new instrument capable of measuring the diameter and form of PCUs up to 20 mm diameter with target uncertainties of 20 nm is being developed. The first stage of this development is the design and construction of an instrument capable of measuring external diameter using two mutually opposed contact probes mounted on precision translation stages. The positions of the probes are measured continuously using two sub-nanometre displacement measuring laser interferometers. The instrument provides a flexible working platform for future developments.