An Analog Front-End Circuit for Noncontact Voltage Measurements, Immune to Input Capacitance

This work presents a novel analog front-end (AFE) circuit for the noncontact voltage measurement (NCVM) of power-line voltages. It introduces a voltage supply driving scheme designed to address the primary challenge of this technique: its sensitivity to the input parasitic capacitance $C_{\text {in}}$ . This capacitance affects the accuracy of the measurement and demands a specific calibration procedure to mitigate its effects. The proposed circuit is insensitive to $C_{\text {in}}$ , thus improving the method accuracy and not requiring an additional calibration procedure. Several tests were performed to validate the solution. Actual noncontact power-line voltage measurements were done using two different capacitive probes with coupling capacitances $C_{X}$ of 3.2 pf and 86 fF, resulting in accuracies of 0.2% $\pm ~0.3$ % and 2.6% $\pm ~0.3$ %, respectively. These accuracy levels are mainly determined by the uncertainties of the measurement instruments instead of the factor $C_{\text {in}}/C_{X}$ as in previous solutions that highly penalize small capacitive probes.