20080197863 | LIQUID PROPERTIES SENSOR CIRCUIT - A sensor circuit is coupled to a sensing element for determining a property, such as a dielectric constant, of a fuel suitable where the dielectric constant is used in determining a concentration of ethanol in the gasoline/ethanol blended fuel. The circuit includes an excitation voltage signal generator, a synchronization trigger and a processing circuit configured to generate an output signal indicative of the fuel property (dielectric constant). The excitation voltage signal is applied to the sensing element to produce an induced current signal therethrough. The synchronization trigger is configured to generate a trigger signal when the excitation voltage signal crosses zero volts, at which time the real (resistive) component of the induced current signal is zero. The induced signal is therefore wholly representative of the imaginary component attributable to a capacitance of the sensing element in sensing relation with the fuel, which in turn is dependent on the dielectric constant (and thus ethanol concentration) of the fuel blend itself. The processing circuit is configured to sample the induced signal in response to the trigger signal and produce the output signal. The synchronization scheme provides for a simplified circuit arrangement since there is o need to decompose a signal combining real and imaginary components. | 08-21-2008 |