Capacitive type converter device
First Claim
1. A capacitive type converter device comprisingvariable condenser having a capacitance variable in response to a value to be measured;
- reference condenser having a capacitance fixed independent of said value to be measured;
oscillator means for supplying an oscillation output to said variable condenser and to said reference condenser;
first rectifying circuit comprising an operational amplifier having an inverting input terminal connected to said variable condenser, and having a non-inverting input terminal connected to a reference point, said first rectifying circuit producing an output;
second rectifying circuit for rectifying a current flowing through said reference condenser, said second rectifying circuit producing an output; and
control means for controlling said oscillation output of said oscillation means in response to said output of said first rectifying circuit or in response to said output of said second rectifying circuit together with said output of said first rectifying circuit, whereby an output signal representative of the capacitance of said variable condenser is obtained from said second rectifying circuit, or an output signal representative of the difference between the capacitance of said reference condenser and the capacitance of said variable condenser is obtained from said outputs of said first and second rectifying circuits.
2 Assignments
0 Petitions
Accused Products
Abstract
A capacitive type converter device, such as used for measuring pressure, comprising first and second rectifying circuits, each including an operational amplifier with a non-inverting input terminal connected to a reference point, to which a variable condenser is connected, the variable condenser having a capacitance which varies in response to a force being measured, such as pressure, and to which a reference condenser is connected, the reference condenser having a capacitance which is fixed independent of the force being measured. The device further comprises an oscillator, whose oscillation output is applied to the variable and reference condensers,and which is controlled by a control means in response to output of the first rectifying circuit, or in response to the output of the second rectifying circuit together with the output of the first rectifying circuit, whereby an output responsive to the capacitance of the variable condenser is obtained from the output of the second rectifying circuit, or an output relating to the difference between the capacitances of the condensers is obtained from the outputs of the first and second rectifying circuits. The device eliminates adverse influences of stray capacitances, non-linearity, offset signals, and parallel capacitances and forward voltages.
26 Citations
10 Claims
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1. A capacitive type converter device comprising
variable condenser having a capacitance variable in response to a value to be measured; -
reference condenser having a capacitance fixed independent of said value to be measured; oscillator means for supplying an oscillation output to said variable condenser and to said reference condenser; first rectifying circuit comprising an operational amplifier having an inverting input terminal connected to said variable condenser, and having a non-inverting input terminal connected to a reference point, said first rectifying circuit producing an output; second rectifying circuit for rectifying a current flowing through said reference condenser, said second rectifying circuit producing an output; and control means for controlling said oscillation output of said oscillation means in response to said output of said first rectifying circuit or in response to said output of said second rectifying circuit together with said output of said first rectifying circuit, whereby an output signal representative of the capacitance of said variable condenser is obtained from said second rectifying circuit, or an output signal representative of the difference between the capacitance of said reference condenser and the capacitance of said variable condenser is obtained from said outputs of said first and second rectifying circuits. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A capacitive type converter device comprising
a variable condenser having a capacitance which varies in response to a force to be measured; -
a reference condenser having a capacitance which is fixed independent of said force to be measured; an oscillator for applying an oscillation output to said variable condenser and to said reference condenser; a first rectifying circuit including rectifying diodes for detecting an alternating current flowing through said variable condenser in the form of a DC signal; a second rectifying circuit including rectifying diodes for detecting an alternating current flowing through said reference condenser in the form of a DC signal; a circuit for computing the difference between said outputs of said first rectifying circuit and said second rectifying circuit, and for providing an output representing said difference; a temperature compensation circuit including a temperature sensor for generating a temperature compensation signal representative of the difference between an ambient temperature and a reference temperature; and control means for controlling said oscillation output of said oscillator to maintain unchanged the sum of said output of said first rectifying circuit and said output of said temperature compensation circuit.
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Specification