Electrometer Charge Scale Calibrations

Electrometers are calibrated by being placed in series with a known capacitance, voltage source, and current limiting resistance. The capacitor is NIST traceable and stable to 10 ppm. The voltage is monitored by a high quality DMM. The equation Q=CV is then used to determine the amount of charge that passed through the electrometer to achieve equilibrium. Some electrometers cannot be calibrated in this manner and are instead calibrated using a current source and a timer. The total uncertainty in charge scale calibrations is approximately 0.1% for high quality equipment.