No contact means no headaches in position transducing

An alternative to traditional resistive potentiometers is a noncontacting device that uses capacitive coupling instead of moving mechanical parts. It consists of a fixed resistive track of conductive plastic and a moving probe. An ac voltage is applied to the track and the probe picks off a current, called a displacement current, by capacitive coupling. To avoid the need for a trailing contact cable, the displacement current is transmitted to a parallel collector track. Although the basic principle of this system is not new, the fact that the coupling capacitances vary with track position has never been taken into account before.