Electrostatic potential measurement of floating conductive objects: Some theoretical considerations and experimental results

The measurement of electrostatic potentials of floating conductive objects can, in principle, be performed by well-known basic experimental setups. Commercial equipment is readily available and the physical principles underlaying the problem are well established. However, electrostatic measurements require special attention, as significant errors can arise from the influence of the measuring setup or the misinterpretation of the results. First, the specificity of the measuring equipment must be well understood such as the difference between field mills, induction probes and feedback probes (also called electrostatic probes). These instruments create specific boundary conditions around the object being measured such as the introduction of grounded planes or the cancellation of the electric field. This influence is particularly significant when measuring floating objects as, for example, belts and suspended or flying objects. Even when results are provided directly in volts, their interpretation varies greatly depending on the instrument used. In the case of the field mills measurements, a calibration must be performed to convert the measured electric field into the potential of the floating object. This calibration is often performed by applying a known potential to the floating object. However, this procedure may introduce errors in the measured values due to the presence of the high voltage cable used to charge the object. We describe some examples of numerical calculations and show some experimental measurements on a levitating object.