Investigating linearity of a high voltage capacitance bridge

High voltage capacitance bridge can be calibrated at fixed ratios using traceable standard capacitors. Typical ratios to be calibrated are 10 to 1 and 100 to 1. Substitution method can be used to reduce bridge related errors and uncertainties. When a capacitor under calibration deviates significantly from the reference capacitor, substitution method is not any more applicable and linearity of a capacitance bridge has to be considered. This paper describes a method to investigate linearity of a high voltage capacitance bridge. The method is based on two reference capacitors and two simultaneously sampling voltmeters. Results of the linearity test of four largest decades of a current comparator capacitance bridge are presented.