Pressure comparison from 25 MPa to 260 MPa between the MSL and the NML

This paper describes a pressure comparison, covering the range 25 MPa to 26 0 MPa, carried out between the CSIRO National Measurement Laboratory (:NML, Australia) and the Measurement Standards Laboratory of New Zealand (MSL) i n 1997 and 1999. A feature of each part of the comparison was the high-reso lution Digiquartz pressure transducer used as the transfer standard. This; small and relatively inexpensive transducer is easier to transport between countries than a bulky and heavy pressure balance. The measured performance of the transducer demonstrates that it can compare the pressure scales of each laboratory to a standard uncertainty of 2.3 kPa, which is much smaller than the uncertainties specified for each pressure scale. The results of b oth comparisons show that the two pressure scales agree to within their res pective uncertainties, although the 1999 comparison produced a larger diffe rence than the 1997 comparison. This may indicate a change in the pressure balance parameters or that the transducer performance is not yet fully char acterized. An analysis is presented to show the relationship between the me asured pressure difference and the parameters of each pressure balance.