Intercomparison of NIST, NPL, PTB, and VSL thermal voltage converters from 100 kHz to 1 MHz

Coaxial, thermal voltage converters were hand-carried among NIST, NPL, PTB, and VSL for comparison of AC-DC difference from 100 kHz to 1 MHz. The highly varied methods and underlying principles on which AC-DC difference determinations are based in each laboratory, the transport standards used, and the results of the comparisons are presented. The AC-DC differences reported by the participating laboratories are in very good agreement. It is concluded that representative values of AC-DC difference in the 100 kHz to 1 MHz frequency range are established with 2 sigma uncertainties of 4-8 ppm. >