Current and frequency range extension of AC-DC current tranfer difference measurement system at CMI

Abstract

This paper describes current and frequency range extension of AC-DC current transfer difference measurement system in CMI which is now able to measure AC-DC current differences from 1 mA up to 10 A in the frequency range 10 Hz -100 kHz.

New generation of cage-type current shunts developed using model analysis

“…The number, value and type of resistors are different in each shunt (see Table 1). The temperature coefficient of the shunts was reduced by using a suitable combination of resistors S102 with different temperature coefficients (one third of S102C and two thirds of S102K), except for the 30 mA shunt with Z201 resistors, which temperature coefficient is below 1 ppm/K [6], [8].…”

“…The ac-dc difference of the shunts was measured using an automated measurement system developed for the ac-dc current transfer difference set up (see Figure 11), which was established in 2008 [6] and improved in 2010 [8].…”

“…Ac and dc currents are applied through a transconductance amplifier Clarke&Hess 8100, which is alternately connected to a dc and ac voltage source (multifunction calibrators Fluke or Datron) using an automated switch OFMET. The standards are comprised of a shunt loaded by a thermal converter [8].…”

“…The uncertainty budget of such a complicated measurement set up covers contributions of the reference standard and its level dependence, the reproducibility of the measured ac-dc difference (standard deviation), influences of the series connection of both standards and measurement set up, the frequency dependence, and the influence of temperature. A detailed description of the uncertainty calculation can be found in [8].…”