Control system for use in the measurement of ultrasmall torques

A control system is described which is one of the major functional subdivisions of the apparatus in an experiment to measure Newton's universal gravitational constant G . In this experiment small masses are allowed to accelerate toward larger masses for a relatively long period of time. From the measured acceleration and the known magnitude of the masses, the gravitational force can be determined. The distance between the masses is maintained essentially constant by utilizing a rotary table on which the masses are mounted in such a way that the small masses are free to move or rotate toward the larger masses which are fixed with respect to the table. The purpose of the control system is to maintain the angle and, therefore, maintain a constant distance between the fixed and movable mass systems. Tracking errors between the mass systems of less than one second of an arc have been maintained.