CAPACITY SENSOR AND CAPACITY MEASURING METHOD

PROBLEM TO BE SOLVED: To provide a capacitance sensor obtaining an absolute value of capacitance change which can detect capacitance change with high sensitivity by obtaining an oscillation curve through changing of the frequency of voltage applied to an object by the use of a variably frequency type oscillator. SOLUTION: A signal of a variable frequency type oscillator 14 is transmitted to a secondary coil 7 from a primary coil 6 through mutual induction. The coil 7 is connected to the capacitance C1 to be measured in series. A spray capacitance C2 exists in parallel with the capacitance C1. The output of tertiary coil 8 to be connected to the coil 7 is detected by a peak detector composed of diode 9, capacitor 10, resistor 11. This signal is amplified 12 and inputted to a personal computer 15. The computer 15 stores an output signal corresponding to the oscillation frequency at that time, and by frequency change, obtaines an oscillation curve from the relation between the frequency and the output. In the case of obtaining the capacitance of an object to be measured continuously, since the resonance frequency and the oscillation curve are always obtained, an absolute value of the capacitance of the object can be obtained.