Capacitive voltage probe for non-contact measurement of common-mode voltage

Capacitive voltage probe is described that can measure the common-mode voltage on a cable without touching its conductor. This capacitive voltage probe has with two coaxial electrodes; the inner electrode works as a voltage pickup, and the outer one shields the inner electrode. These electrodes separate into two parts for damping to the cable. Using a high input impedance circuit, this probe measures the common-mode voltage by detecting the voltage difference between the two electrodes. The probe's characteristics were evaluated by measuring its linearity and frequency response. The results show that this probe has a dynamic range of 100 dB and flat frequency response from 10 kHz to 30 MHz. Errors in measurement due to the position of the cramped cable in the inner electrode and to differences in the cable radius were evaluated theoretically and experimentally. The results indicate that the influence of the cable position is small and the deviation in sensitivity induced by differences in the cable radius can be calibrated using compensatory data.