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

A coaxial ac shunt with calculable ac-dc difference

“…In principle, a resistor used in ac can be thought to be equivalent to a dc resistance R dc in series with a inductance L and paralleled with a capacitance C. It was shown in Fig 1. The time constant of the ac resistor and the ac-dc difference can be expressed in equation (1) and equation (2). (2), we can know that for the lower resistance, the ac-dc difference was dominated by the inductance L, and for the higher resistance, it is dominated by the capacitance C. The basic idea of the design of the coaxial shunt is to find a method to get the known L and C. The resistance of shunt is around 1 Ohm, and the structure of the coaxial shunt is shown in Fig 2. First 16 sets of copper wires were evenly distributed and mounted in the coaxial shunt.…”

“…AC shunts are widely used as the standards for ac-dc current transfer measurements up to 20 A at 100 kHz in most of the national metrology institutes [1] [2]. Thermal converters with the input current around 10 mA were taken as the reference for the start point of the step up procedure.…”

1 A and 120 mA Thin-Film Multijunction Thermal Converters

“…The low current chip [1] dissipates 10 mW in the heater. To achieve approximately the same temperature rise in the 1 A heater with 100 mW dissipated, the chip geometry was dramatically changed.…”

“…As thermal current converters they may be used as standards for current up to 10 mA [1]. For higher currents parallel shunts may be used, but they present problems from both stray capacitance to ground and thermal drifts, and exhibit greater errors from skin effect at 20 kHz and above.…”

Quartz Planar Multijunction Thermal Converter as a New AC-DC Current Transfer Standard up to 1 MHz

“…At lower currents, planar multijunction thermal converters (PMJTC) with heater resistances from 90 Q1 to 960 QL are used in a step-down procedure. Coaxial current shunts in parallel with PMJTCs extend the current range up to 20 A [3].…”