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

This article compares two instruments for the traceable measurement of dc low currents, a custom capacitance-voltage (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-Vsource. Such frequency dependence can also affect primary metrology experiments in other fields.