Capacitive Sensors& Nanometrology
PI capacitive (capacitance) sensors are the metrology system of choice for the most demanding nanopositioning applications. They are absolute-measuring, high-dynamics devices. PI capacitive sensors / control electronics use a high-frequency AC excitation signal for enhanced bandwidth and drift-free measurement stability (subnanometer stability over several hours, see Fig. 6, on Link).
They enable direct measurement of the moving platform and are especially well-suited for multi-axis measurements in parallel metrology configurations. Parallel metrology means that the controller monitors all controlled degrees of freedom relative to "ground", a prerequisite for active trajectory control.
Capacitive sensors also offer the highest linearity (accuracy).