Electrostatic capacitance sensing circuit
First Claim
1. An electrostatic capacitance sensing circuit, comprising;
- (a) resonance means having an electrode capacitance formed by a substance to be measured, a corrosion preventing capacitor for preventing electrolytic corrosion connected in series with the electrode capacitance with respect to a junction point, and an inductance connected to the electrode capacitance and said corrosion preventing capacitor via said junction point;
(b) active element means oscillating at a resonance frequency predetermined by said resonance means; and
(c) capacitive coupling means connected between said junction point of the inductance and the corrosion preventing capacitor and said active element means to prevent a DC voltage from being applied to the electrode capacitance.
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Accused Products
Abstract
The electrostatic capacitance sensing circuit comprises a resonance circuit composed of an electrode capacitance formed by a substance to be measured and sandwiched between two opposing electrode plates and an inductance at least part of which is connected in parallel to the electrode capacitance; an active element (e.g. transistor) for constituting an oscillator in cooperation with the resonance circuit; and in particular a capacitor connected between the resonance circuit and the active element. Since a dc bias voltage of the active element is substantially not applied to the electrode plates, it is possible to prevent electrolytic corrosion of the electrode plates due to electromotive force generated between the electrode plates when ions are resolved into the substance to be measured and therefore the substance changes to an electrolytic solution.
18 Citations
15 Claims
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1. An electrostatic capacitance sensing circuit, comprising;
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(a) resonance means having an electrode capacitance formed by a substance to be measured, a corrosion preventing capacitor for preventing electrolytic corrosion connected in series with the electrode capacitance with respect to a junction point, and an inductance connected to the electrode capacitance and said corrosion preventing capacitor via said junction point; (b) active element means oscillating at a resonance frequency predetermined by said resonance means; and (c) capacitive coupling means connected between said junction point of the inductance and the corrosion preventing capacitor and said active element means to prevent a DC voltage from being applied to the electrode capacitance. - View Dependent Claims (2, 3, 5, 6, 7, 8, 9)
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4. An electrostatic capacitance sensing circuit, comprising:
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(a) resonance means having an electrode capacitance formed by a substance to be measured, a corrosion preventing capacitor for preventing electrolytic corrosion connected in series with the electrode capacitance, and an inductance connected to the electrode capacitance and said corrosion preventing capacitor; (b) active element means oscillating at a resonance frequency determined by said resonance means; and (c) capacitive coupling means connected between an intermediate tap of said inductance and said active element means to prevent a DC voltage from being applied to the electrode capacitance. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification