Noncontact AC Voltage Measurements: Error and Noise Analysis

Abstract

A capacitive noncontact ac voltage measurement technique and its feasibility to measure arbitrary waveform signals are analyzed. The method provides self-calibration of the scale factor, an important feature considering the high variability that coupling capacitances present. The analysis of several errors related to the technique is performed, showing the impact of different design parameters on the final accuracy. Scaling errors due to the electronic circuit can be constrained to less than 0.5%, and can be disaffected, whereas those due to the frequency dependence of cable sheath permittivity can be up to 3% for polyvinyl chloride sheathed cables. This error is not controllable by electronic design but requires working on electrode probe. A noise model is also proposed and experimentally validated, showing that signal-to-noise ratios of up to 100 dB are achievable with common components. A functional prototype was built and tested by acquiring power-line voltage and other arbitrary signals without contact. Instantaneous voltage signals were acquired by the proposed technique and contrasted with those acquired directly. For the measurement of power-line voltage and using the self-calibration feature, the instantaneous error was lower than 7 V (2.2%) for a ±1300 V measurement range at 50 Hz. If manual correction is applied, the error can be reduced to 0.28 V rms (0.12%)