Comparison in the absolute pressure range 100 kPa to 2100 kPa between MIKES and Vaisala Oyj

Centre for Metrology and Accreditation (MIKES) and the Measurement Standards Laboratory of Vaisala Oyj arranged in 2002-2003 a bilateral comparison in the absolute pressure range from 100 kPa to 2100 kPa. The transfer standard was a set of two 2100 kPa absolute pressure transducers. The original procedure for the comparison consisted of three subsequent calibrations: the first one at Vaisala, the second at MIKES and finally the third one again at Vaisala. The intention was to compare the averages of the two Vaisala results to the MIKES results. As there were unexpected deviations in the results, the procedure above was repeated. The results of the second round were much the same as before. Finally, it was found out that the temperature sensitivity of the transfer standards was much higher than expected. Further, the zero stability of one of the transfer standards was not good. The results were corrected for temperature differences and the uncertainty in temperature was taken into account in calculating the measurement uncertainty. Now it could be concluded that the results of MIKES and Vaisala were in a good agreement. The uncertainty level, however, was clearly higher than the best measurement capabilities of the two laboratories. The unexpected features of the transfer standards caused a lot of extra work and several delays in the original schedule of the comparison.