AC-DC current transfer step-up calibration and uncertainty calculation

Abstract

New ac-dc current transfer standards are built for the current range from 0.3 mA to 20 A and the frequency range from 10 Hz to 100 kHz. A 3-dimensional PTB-Multijunction Thermal Converter (MJTC) with a heater resistance of 27 R is the basic standard for the acdc current transfer at currents from 20 mA to 50 mA. At lower currents, planar MJTCs (PMJTCs) with heater resistances from 90 ! 2 to 960 R are used in a step-down procedure. Coaxial current shunts in parallel with PMJTCs extend the current range up to 20 A. The standard measurement uncertainties are in the range from 0.2 yA/A at 25 mA and 1 kHz to 50 pA/A at 20 A and 100 kHz. The high sensitivity of the PMJTC allows bigger steps in the step-up calibration and some smaller steps between these steps. Calibration of all these steps leads to an overdetermined system to check for the validity of the assumptions made in the step-up procedure. This results in reduced uncertainties at the different current levels compared to the old method.

Ac-Dc Characterization of Coaxial Current Shunts and Application of the Shunt in the Digital Sampling Wattmeter

“…The shunts which are used in national metrology laboratories to satisfy required parameters and also analyzed in this paper are cage type designed similar to SIQ AC shunts [4], and are fabricated using double-sided FR4 fiberglass-epoxy PCB material, equipped with N-type connectors, and constructed with three circular PCB elements, crossbars and resistors. Thermal converters are the most accurate standards for the transfer of alternating current to the equivalent dc quantities [5]. A special type of thermal converter is used in this measurement and it is planar multi junction thermal converter (PMJTC (90 Ω)).…”