| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric potential sensor having a simple formation and a stabilized output signal by stabilizing the amplitude of a piezoelectric tuning fork and not decreasing the S/N ratio. SOLUTION: This electric potential sensor 10 includes a piezoelectric tuning fork 11. The piezoelectric tuning fork 11 includes a tuning fork vibrator 11a, and a driving piezoelectric element 11b for driving the vibrator 11a is installed on one arm part of the vibrator 11a, and a feedback piezoelectric element 11c for feedback of a signal to the driving piezoelectric element 11b is installed on the other arm part of the vibrator 11a. A detection electrode 12 is formed on the surface of the other arm part of the piezoelectric tuning fork 11, and the piezoelectric tuning fork 11 is arranged so that the detection electrode 12 will face to a measurement object 13. A circuit block of this electric potential sensor 10 is composed of a self-oscillation oscillating circuit 14 for driving the piezoelectric tuning fork 11 into the self oscillation state, a signal processing circuit 20 for processing and detecting an electric signal obtained from the piezoelectric tuning fork 11, and a comparison circuit 30 for comparing the output signal of the feedback piezoelectric element 11c arranged on the piezoelectric tuning fork 11 with a reference signal. A gain control circuit 14c is included in the self- oscillation oscillating circuit 14.
|
