The effect of pressure-transmitting fluids in the characterization of a controlled clearance piston gauge up to 1 GPa

The present paper describes the effect of different pressure-transmitting fluids (PTFs) on the systematic characterization of an oil-operated controlled clearance piston gauge (nominal diameter of the piston, 2.5?mm) in the pressure range up to 1000?MPa (1?GPa). Pure PTFs and mixtures of different PTFs are studied and four of them will be discussed here: namely (a) pure normal hydraulic oil (J-13), (b) a mixture of J-13 and an aviation turbine fuel (ATF), (JATF), (c) a pure di-ethyl-hexyl-sebacate oil (BIS) and (d) a mixture of white gasoline (G), J-13 and sebacate (GJBIS).The characterization is the measurement of the fall-rate of the piston as a function of applied jacket pressure (pj) with various PTFs using the method of Heydemann and Welch (HW model) (Heydemann and Welch 1975 Experimental Thermodynamics vol II, ed B Leneindre and B Voder (London: Butterworths) p 147). The analysis of the results is the determination of the cube root of the piston fall-rate (v1/3) with pj at different loads or measured pressures (pm). The linear portion of this v1/3?pj curve is extrapolated towards the null value of fall-rate, and the stall jacket pressure (pz) at different pm is obtained. It is observed that reasonably good fall-rate data could be obtained for J-13, JATF and BIS up to maximum pressures of 500?MPa, 700?MPa and 650?MPa, respectively. For GJBIS, these fall-rate data can be obtained up to a maximum pressure of 1?GPa. From the values of pz at different pm and also the values of the jacket pressure coefficient (d) along with other characteristic parameters in the HW model (Newhall et al 1979 Rev. Sci. Instrum. 50 964?8, Bandyopadhyay and Olson 2006 Metrologia 43 573?82), we have determined the relative standard uncertainties in the effective area (u(Ae)/Ae) for GJBIS up to 1?GPa for pj = 0 (free deformation mode) and pj/pm = 0.3. It is interesting to note that for pj = 0, at a pm of 100?MPa, u(Ae)/Ae is 74 ? 10?6, while at a pm of 1?GPa, u(Ae)/Ae is 248 ? 10?6. However, for pj/pm = 0.3, at a pm of 100?MPa, u(Ae)/Ae is 67 ? 10?6, while at a pm of 1?GPa, u(Ae)/Ae is 125 ? 10?6. A comparative study of u(Ae)/Ae has been elaborated with the four PTFs investigated. We have shown that at a pm of 100?MPa, u(Ae)/Ae is 202 ? 10?6, 114 ? 10?6, 66 ? 10?6 and 67 ? 10?6, for J-13, JATF, BIS and GJBIS, respectively, while at a pm of 500?MPa, u(Ae)/Ae is seen to be 97 ? 10?6, 57 ? 10?6, 46 ? 10?6 and 56 ? 10?6 for J13, JATF, BIS and GJBIS, respectively. Our measurements show that GJBIS is a convenient PTF for working up to 1?GPa. Finally, the results of the characterization are compared with the NPLI pressure scale through calibration of a NPLI secondary standard which is traceable to the LNE (France) pressure scale though direct comparison and participation in a recently concluded bilateral comparison with NIST (USA).