Comparison of Low DC Current Traceability Methods and Gas Capacitors AC–DC Dependence

Abstract

The paper compares two instruments for traceable measurement of dc low currents, a custom capacitancevoltage (C-V ) source and the Ultrastable Low-Current Amplifier (ULCA), a commercial precision transresistance amplifier. The instruments are calibrated through independent traceability routes. The comparison base relative accuracy is in the 10 −6 − 10 −5 range. Differences between the two instrument readings, in the 10 −5 range, are interpreted as an effect of the frequency dependence of the capacitor employed in the C-V source. Such frequency dependence can affect also primary metrology experiments in other fields.