INTERCOMPARISON OF NIST, NPL, PTB, AND VSL THERMAL VOLTAGE CONVERTERSFROM 100 KHZ TO 1-MHZ

Coaxial, thermal voltage converters were hand-carried among NIST, NPL, PTB, and VSL for intercomparison of ac-dc difference from 100 kHz to 1 MHz. This paper briefly describes the highly varied methods and unde rlying principles on which ac-dc difference determinations are based i n each laboratory, the transport standards used, and the results of th e intercomparisons. The ac-dc differences reported by the participatin g laboratories are in very good agreement. It has been concluded that representative values of ac-dc difference in the 100 kHz to 1 MHz freq uency range have been established with 2sigma uncertainties of 4-8 ppm .