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

Abstract

This work presents a novel analog front-end circuitfor the non-contact voltage measurement of power-line voltages.It introduces a voltage supply driving scheme designed toaddress the primary challenge of this technique: its sensitivity tothe input parasitic capacitance Cin. This capacitance affects theaccuracy of the measurement and demands a specific calibrationprocedure to mitigate its effects.The proposed circuit is insensitive to Cin, thus improving themethod accuracy and not requiring an additional calibrationprocedure. Several tests were performed to validate the solution.Actual non-contact power-line voltage measurements were done byusing two different capacitive probes with coupling capacitancesCX of 3.2 pf and 86 fF, resulting in accuracies of 0.2±0.3%and 2.6±0.3% respectively. These accuracy levels are mainlydetermined by the uncertainties of the measurement instrumentsinstead of the factor Cin/CX as in previous solutions that highlypenalize small capacitive probes.