| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric potential sensor which is stable in output signal even when the amplitude of a piezoelectric tuning fork or the permittivity of air is changed. SOLUTION: An electric potential sensor 10 includes a piezoelectric turning fork 11 as a mechanical oscillating means. The piezoelectric tuning fork 11 includes an oscillating body 11a of the tuning fork type, a driving piezoelectric element 11b to drive the oscillating body 11a is provided on one arm part of the oscillating body 11a, and a feedback piezoelectric element 11c to feed back the signal to the driving piezoelectric element 11b is provided on the other arm part of the oscillating body a. A detection electrode 12 is formed on the surface of the other arm part of the oscillating body 11a, and the piezoelectric tuning fork 11 is arranged opposite to a work 13 to be measured. A monitoring electrode 15 is formed on the surface of one arm part of the oscillating body 11a, and a monitoring body 16 charged to the reference voltage Vm is arranged opposite to the monitoring electrode 15.
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