Final report on key comparison CCAUV.U-K3.1

In October 2013, during the 9 th meeting of the CCAUV in Sevres, France, the result s of the key comparison CCAUV.U-K3 were presented and the Draft B report wa s agreed upon shortly thereafter by email. The results have also been published in the meantime [1 ]. During the meeting it was decided to start a new comparison CCAUV.U-K3.1 to give all participants of the preceding loop who delivered discrepant values the opportunity to perform new measurements. In add ition, NMIJ was included since the institute could not take part in CCAUV.U-K3 because of the horrible earthquake in 2011. Furthermore, NMC A*STAR had asked for the opportunity to take part, but resigne d later from the comparison. The goal of the key comparison was to show the capa bilities of the participating laboratories to deter mine the acoustic radiation conductance of an ultrasonic transducer by measuring the total time-averaged ultrasonic power emitted for an applied rms voltage in the nominal frequency range from 2 MHz to 16 MH z and for nominal output power values between 10 mW a nd 15 W. Although the ultrasound power is the measurand of the key comparison, the participants w ere asked to report the radiation conductance which is independent of the applied voltage and is theref ore a characteristic property of the transducer at a particular frequency. Nevertheless, the key compari son primarily represents the ultrasound power measurement capabilities of the participating NMIs and is suitable for justifying CMC entries of this variable. This key comparison was planned and conducted accor ding to the “Guidelines for CIPM Key Comparisons” issued by the BIPM [2].