Patent ID: 6316942
Filing Date: 2001-11-13
Classification: G01R

Abstract:
An electric potential sensor, comprising:a piezoelectric tuning fork provided with a vibrating body of tuning fork type, a driving piezoelectric element provided on a first arm of said vibrating body, and a feedback piezoelectric element provided on a second arm of said vibrating body;a detection electrode provided on said piezoelectric tuning fork;a signal-processing circuit connected to said detection electrode which detects the change in the electric signal generated in said detection electrode which is attributable to the charge on the surface of an object to be measured;a comparator receiving a feedback signal from said feedback piezoelectric element and outputting a signal obtained by comparing said feedback signal to a reference signal; anda self-oscillation circuit connected between said feedback piezoelectric element and said driving piezoelectric element and receiving said feedback signal and outputting a driving signal to said driving piezoelectric element, said self-oscillation circuit including a gain control circuit which receives said signal from said comparator and controls an amplitude of said driving signal.