Characterization of a compact 200 MPa controlled clearance piston gauge as a primary pressure standard using the Heydemann and Welch method

Controlled clearance piston gauges are used as primary pressure standards at many national metrology institutes. The National Institute of Standards and Technology, in collaboration with the National Physical Laboratory ( India), is studying the performance of a new generation of controlled clearance gauges that offer the potential for reduced uncertainties. The gauges are also well suited to interlaboratory comparisons because of their smaller, integrated design and use of existing mass sets. In this paper we present results of the characterization of a 200MPa oil-operated controlled clearance gauge with a 2.5 mm nominal diameter piston and cylinder. The gauge is operated with an external cylinder pressure of 0 MPa to 80 MPa. We present results of piston fall rate measurements, deformation measurements, piston diameter measurements and modelling calculations using the Heydemann - Welch (HW) method on two occasions over a two-year time period. The relative standard uncertainties in the effective area (A(e)) using the HW method range from 24 x 10(-6) at 20 MPa to 37 x 10(-6) at 200 MPa. We have compared results of the HW method to the present NIST hydraulic pressure scale. For the entire pressure range, there is agreement in A(e) within the combined standard uncertainty (k = 1)