A Current Source for Picoamperemeter Calibration

A traceable current source for the calibration of low-current meters (picoamperemeters, electrometers) in the 100fA-100pA current range is here presented. It is based on a low-frequency trapezoidal wave generator, measured with a sampling voltmeter, which charges and discharges a gas-dielectric capacitor. The generated current is traceable to units of voltage, capacitance and time. The source will be employed to extend in the lower range the Italian national standard of dc current, and for the Italian participation in the EUROMET. EM-S24 international intercomparison. Being simple and inexpensive, the source can find application in secondary calibration laboratories.