EXTENSION OF THE NIST AC-DC DIFFERENCE CALIBRATION SERVICE FOR CURRENT TO 100 KHZ

The NIST calibration service for ac-dc difference of thermal current c onverters relies on multijunction thermal converters as the primary st andards, and various thermal converters and thermoelements (TEs) as th e reference and working standards. Calibrations are performed by compa ring the ac-dc difference of a customer's thermal current converter to the ac-dc difference of a NIST standard current converter. Typical ar tifacts accepted for calibration include single-junction thermoelement s. multijunction thermal converters, and transfer shunts for use with TEs. This paper describes the standards on which the calibration servi ce is based and the results of the study to characterize the NIST stan dards over the extended frequency range from 50 kHz to 100 kHz at curr ents from 1 mA to 20 A. The general method for the frequency extension at high frequency involves the use of thermoelements in the 5 mA rang e, with small frequency dependence, as the starting point for build-up and build-down chains to cover the whole range from 1 mA to 20 A.