A PID control system for calibration of test of gravitational inverse square law at millimeter ranges

Due to its high sensitivity to weak forces, the classical torsion pendulum was widely employed in the fields of precision gravitational measurement, which can be evaluated by testing of Newtonian inverse square law (ISL). In order to get much higher precision for the tests of ISL at short ranges, such as at millimeter and/or sub-millimeter level, the torsion pendulum cannot work precisely in free oscillation motion due to the electrostatic disturbance. This paper presents a method using proportional-integral-differential (PID) technology to make pendulum to keep quasi-static. A closed-loop system with PID controller is realized and calibration results show the system has the potential to get the precision of test of the ISL violation at the order of 10
⁻¹⁶
N·m at millimeter range.