Capacitive feedback transducer and closed loop instrument meter mechanism

Abstract

A display pointer is driven back and forth along a predetermined path by a geared-down miniature d.c. servomotor in accordance with a command signal. The path is determined by an elongated printed circuit board base having closely adjacent, elongated, coextensive triangularly shaped plates thereon, constituting stationary capacitor plates of a pair of variable capacitors. The printed circuit board includes a dielectric material which also overlays the triangular plates. A relatively narrow, electrically conductive slider member extends laterally across the triangular plates and is supported by and rides on the printed circuit board and constitutes a common movable capacitor plate for the variable capacitors. The display pointer is attached to and positioned by the slider. The slider in turn is displaced along the printed circuit board by means of a cable and pulley mechanism coupled to the servomotor. The pair of variable capacitors are electrically connected with a pair of diodes in balanced bridge fashion in order to provide a signal proportional to the position of the slider along the path. The position signal is fed back and summed with the command signal to provide an error signal for controlling the servomotor.