Method and circuitry for measuring the impedance of a sensor
First Claim
1. Method of measuring the impedance of a sensor by a sine-shaped AC voltage of defined frequency comprising the steps ofgenerating a square wave voltage in synchronism with the sine-shaped AC voltage;
- applying the sine-shaped AC voltage to a measuring circuit containing said impedance;
modifying the resulting AC voltage proportional to said impedance in a selective circuit of a defined phase-frequency- and amplitude-frequency characteristic, thereby bringing said AC voltage into a defined phase relation to said square wave voltage;
rectifying the modified AC voltage and transforming it into a DC voltage proportional to said impedance in a rectifier- and low-pass circuit, said rectifying and transforming step being affected by intermittently short-circuiting a grounded resistor of said rectifier- and low-pass circuit by means of a switch controlled by said square wave voltage.
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Accused Products
Abstract
A method of measuring the impedance of a sensor by applying a sine-shaped AC voltage and transforming the response signal proportional to said impedance into a DC voltage such that even for very little measured voltage highest linearity is present. The method comprises the steps of generating a square wave voltage together and in synchronism with said AC voltage, applying said AC voltage to said sensor impedance, filtering the resulting AC voltage and bringing it into a defined phase relation to the square wave and rectifying the AC voltage by means of a switch controlled by said square wave. The rectifier circuit is a low-pass circuit having a grounded resistor which by said switch intermittedly is short-circuited.
37 Citations
8 Claims
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1. Method of measuring the impedance of a sensor by a sine-shaped AC voltage of defined frequency comprising the steps of
generating a square wave voltage in synchronism with the sine-shaped AC voltage; -
applying the sine-shaped AC voltage to a measuring circuit containing said impedance; modifying the resulting AC voltage proportional to said impedance in a selective circuit of a defined phase-frequency- and amplitude-frequency characteristic, thereby bringing said AC voltage into a defined phase relation to said square wave voltage; rectifying the modified AC voltage and transforming it into a DC voltage proportional to said impedance in a rectifier- and low-pass circuit, said rectifying and transforming step being affected by intermittently short-circuiting a grounded resistor of said rectifier- and low-pass circuit by means of a switch controlled by said square wave voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification