DETECTOR FOR VARIATION IN ELECTROSTATIC CAPACITANCE
Document Type and Number:
Japanese Patent JP3233791
PURPOSE: To accurately detect physical quantities and the like by providing an integrator setting the difference between the electrostatic capacitance of a detector corresponding to physical and chemical quantities of the detecting object and a reference capacitance as a part of constants, and an oscillator circuit determining the oscillation frequency from the capacitance difference.
CONSTITUTION: Positive side input terminal of an operation amplifier 1 of a differential capacitance reversal integrator is grounded, a resistor R is connected to the negative side of the input terminal, and between the output terminal and the negative side of the input terminal, a reference capacitance CR directly connected by a reversal amplifier 2 (with gain -K) as a feedback element and a sensor capacitance CS are connected in parallel. Thereby, an integrator setting the difference between the reference capacitance CR and the sensor capacitance CS as a part of constants is formed, The output VOUT of a state variation type BPF circuit with the use of this integrator is connected to the input VIN to make a harmonic oscillator circuit. The oscillation frequency is determined by the difference between the capacitances CR and CS. Therefore, even when the variation of capacitance CS is small, the variation of various physical quantities or chemical quantities can be accurately detected.
September 21, 2001
August 25, 1994
YAMATAKE HONEYWELL CO LTD
G01B7/00; G01D5/24; G01L13/06; G01N27/22; G01R27/26; G01B7/00; G01D5/12; G01L13/00; G01N27/22; G01R27/26; (IPC1-7): G01R27/26; G01B7/00; G01D5/24; G01L13/06; G01N27/22