Proficiency testing through interlaboratory comparison in the pressure range up to 70 MPa using pressure dial gauge as an artifact

The proficiency testing (PT), a quality control, provides an additional means to ensure quality of laboratory testing results. The primary objective of organizing PT is to assess laboratory's technical competence to perform measurements. This paper describes PT of 11 laboratories, nine accredited by National Accreditation Board for Testing and Calibration of Laboratories (NABL), having best measurement capabilities (< 0.25 % of full-scale pressure) by means of interlaboratory comparison using pressure dial gauge (5-70 MPa) as an artifact. This programme was identified by code number NABL-Pressure-PT003. National Physical Laboratory (NPLI), New Delhi coordinated this programme (February 2003-March 2004) and acted as a reference laboratory. The comparison was carried out at 14 arbitrarily chosen pressure points (5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 and 70 MPa) throughout the entire pressure range (5-70 MPa). Out of the total 145 measurement results, 86 (59.31 %) results were found in good agreement with the results of reference laboratory, NPU, New Delhi. The relative deviations of the laboratories values with reference values were found almost well within the uncertainty band of the reference values (44.14 % pressure points), within their combined uncertainty band (59.31% pressure points) and within their best measurement capabilities (80.34 % pressure points). Since most of the laboratories have underestimated their measurement uncertainties, 40.69 % measurement results were found out of the combined uncertainty band during this comparison. Overall, results were reasonably good being the first PT for all the participating laboratories. This exercise gives an opportunity to calibration laboratory to demonstrate its technical competence of routine calibration services rendered to clients and to have the measurement traceability to the national metrology institute, NPLI, New Delhi.