A multi-electrode plane capacitive sensor for displacement measurements and attitude controls

A novel, multi-electrode capacitive sensor has been designed, realized and tested at INRiM (Istituto Nazionale di Ricerca Metrologica). The circular active electrode of a guarded plane-parallel capacitive sensor is sub-divided into four sectors of equal area. The four output signals from each independent sensor are acquired, normalized and summed, to obtain the displacement. Similarly, by a combination of summing and differencing, the tip and tilt between the relative electrodes can be determined. An angular sensitivity up to 70mV/μrad with a noise level of approximately 85 μV Hz−1/2 has been achieved with a working distance of 50μm. The angular sensitivity decreases to a few mV/μrad for plate separations larger than 200μm. The measuring electronics was set for a full-scale displacement range of several hundreds of micrometers.