Metrological Equivalence of National Hydraulic Pressure Standards in Regional and Global Measurement System

The present paper describes the current status of hydraulic pressure standards, their traceability, calibration services and activities for ensuring the reliability. In order to improve the reliability of these standards, to provide objective evidences of the technical competence and to build-up and maintain mutual confidence of national hydraulic pressure standards, an extensive inhouse laboratory intercomparison is carried out in a systematic manner The present paper describes the summary of the results thus obtained in this in-house laboratory intercomparison exercise of 10 national hydraulic pressure standards and their associated measurement uncertainties. The intercomparison of these pressure standards is carried out using an internationally accepted method of cross-floating of piston gauges. The NPLI has also participated in many bilateral, regional and international key comparisons in the past. The main aim of the present paper is to present the current status of Indian notional hydraulic pressure standards established at NPLI, their measurement capabilities with associated uncertainties, the CMCs registered in Appendix 'C' of BIPM and results of the key comparisons, specially included in Appendix 'B' of Key Comparison Database (KCDB) of BIPM. NPLI, India has also implemented the quality system in the laboratory and the peer review of 5 CMCs, in hydraulic pressure region, has successfully been completed during February, 2009 as per ISO 17025. The international benchmarking of CMCs and our experiences during peer review in pressure standards are also described in this paper In the future, the NPLI plans to continue technical development in order to be able to provide the pressure standards required by the markets which con support advanced industrial technology. Efforts in this direction would be focused on the establishment of new standards for the differential hydraulic pressure measurements up to 50 MPa or more.