A SELF-CONTAINED FLOATING SPHERICAL PROBE FOR THE MEASUREMENT OF VOLUME ELECTRIC-FIELDS

A self-contained, electrically floating, spherical electric field prob e which is capable of measuring DC electric fields in volume regions h as been developed. The spatial field variation must occur on a length scale larger than the sphere diameter. The sphere floats to the local potential existing in its absence, perturbing the ambient field in a p recisely known way, thus providing a means to measure volume fields-wi thout ambiguous perturbations. The sphere is also capable of measuring its own collected charge which can be used to infer the polarity and magnitude of ions or other space charge in the probe vicinity. The 15 cm diameter aluminum sphere contains six miniature 800 Hz vibrating ca pacitor sensors, a synchronous detection data acquisition system with A/D converter, and a digital fm transmitter operating at 50 MHz. Data is sent at 1200 baud to a nearby receiver and computer for interpretat ion and processing. The sensor data, processed in real time, provide v alues of ambient field magnitude and collected sphere charge. The prob e can measure fields as low as 50 V/m and can operate for several hour s on one set of batteries.