Revised characterization of the controlled clearance piston gauge

Abstract

A revised equation is presented for the effective piston area of controlled clearance deadweight testers from the theory of elasticity which accounts for the semi-infinite loading of the measured pressure cylinder. The concept of pressure transmissibility expressed in terms of transmission delay threshold pressure and the importance in the choice of operating fluids is discussed. Test results illustrating pressure transmissibility for 25 different fluids at pressure between 138 MPa ͑20 000 psi͒ and 1380 MPa ͑200 000 psi͒ are presented, together with proposed ranking of the fluids based on their relative pressure transmissibility. The linear nature of the stall curve with fluids of high transmissibility and the resulting linear nature of the adjustments to the effective area are shown. The linearity allows the use of considerable extrapolation for making reasonable estimates of effective area, where direct knowledge of the slope of the stall curve is not known. The robustness of the new equation is demonstrated by applying the equation to data from two mercury point experiments at Harwood ͑9 years apart͒, several National Institute of Standards and Technology ͑NIST͒ characterizations of controlled clearance gauges, some other experiments at Harwood, and the data from NIST's experiment using a controlled clearance piston gauge to isolate the transition pressure of bismuth from Bi I to Bi II. The conclusions reached indicate that with suitable operating fluids, there is a negligibly small difference between pressure values calculated from the method discussed here and that used by NIST based on experimental determination of the jacket pressure coefficient.