A Step-Down Technique to Calibrate AC Current Down to 10 μA Using a Precision 10 mA Current Shunt

This paper describes a calibration procedure for AC current measurements at 1 mA, 100 µA and 10 μA using a NIST-calibrated 10 mA current shunt as a reference standard. The procedure involves a step-down technique using the reference transfer standards (RTS) as a precision current divider. The RTS is used at values of 370 Ω, 3.3 and 30 kΩ to provide the intended currents. Uncertainty calculations are estimated for calibrating the AC current of 10 mA, 1 mA, 100 μA and 10 μA at 55 Hz and 1 kHz. The expanded uncertainties are around the values of 37 nA and 1 nA for the ranges of 1 mA–10 μA respectively.

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