Abstract
The paper reviews the various methods employed in the precise measurement of differential pressure at high line pressure. Included is the new NPL primary standard in this field, its method of use and the uncertainties of measurement associated with it.
As primary standard instruments are not readily portable, various commercial instruments have been studied at NPL to evaluate their performance as transfer standards. Descriptions of three devices tested and a summary of the results obtained are given.
NPL can now offer as a service to industry, the calibration of high quality differential pressure gauges at high line pressure. For measurements made at NPL the total uncertainty (expressed at the 95% confidence level) in the differential pressure ΔP over the range 25 kPa to 250 kPa and for line pressures up to 15 MPa, is ±(0.008% ΔP + 5 Pa). For measurements made away from NPL using a transfer standard the total uncertainty is increased to ±(0.01% ΔP + 30 Pa) for a single observation.
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