Capacitive fuel composition sensor with slow oscillator and high speed switch
First Claim
1. A fuel composition sensor for a fuel mixture in a fuel supply line for a combustion engine wherein the fuel mixture comprises two fuels of different dielectric constants in unknown relative concentrations, at least one of the fuels being electrically conductive, the sensor comprising, in combination:
- a sensor capacitor in the fuel line adapted for fuel flow therethrough so that the fuel mixture provided to the engine comprises a dielectric which determines the capacitance thereof but also comprises a capacitor shorting electrical conductance;
a reference capacitor of constant capacitance in series with the sensor capacitor to form therewith a voltage divider having an output junction; and
circuit means comprising a square wave oscillator with an output high speed switching MOSFET connected in series with a resistance across an electric power supply, the reference and coupling capacitors being connected in series across the MOSFET with the coupling capacitor having an electrode connected to the junction of the resistance and MOSFET, the circuit means being effective to repetitively produce, at a comparatively low frequency, a predetermined fast voltage change across the series combination of the reference and sensor capacitors to produce a corresponding voltage change at the output junction comprising an initial voltage change essentially proportional to the capacitance ratio of the sensor and reference capacitors followed by an opposite voltage change due to leakage current through the fuel mixture, whereby the initial voltage change indicates the fuel composition.
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Accused Products
Abstract
A fuel composition sensor provides to a voltage divider comprising sensor and reference capacitors a voltage which oscillates between two voltages at a comparatively low frequency, such as 6 KHz, for lower power dissipation, but which switches fast to produce periodic fast voltage changes across the voltage divider to produce voltage spikes at the junction of the capacitors indicative of the capacitance ratio and thus of fuel composition.
67 Citations
8 Claims
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1. A fuel composition sensor for a fuel mixture in a fuel supply line for a combustion engine wherein the fuel mixture comprises two fuels of different dielectric constants in unknown relative concentrations, at least one of the fuels being electrically conductive, the sensor comprising, in combination:
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a sensor capacitor in the fuel line adapted for fuel flow therethrough so that the fuel mixture provided to the engine comprises a dielectric which determines the capacitance thereof but also comprises a capacitor shorting electrical conductance; a reference capacitor of constant capacitance in series with the sensor capacitor to form therewith a voltage divider having an output junction; and circuit means comprising a square wave oscillator with an output high speed switching MOSFET connected in series with a resistance across an electric power supply, the reference and coupling capacitors being connected in series across the MOSFET with the coupling capacitor having an electrode connected to the junction of the resistance and MOSFET, the circuit means being effective to repetitively produce, at a comparatively low frequency, a predetermined fast voltage change across the series combination of the reference and sensor capacitors to produce a corresponding voltage change at the output junction comprising an initial voltage change essentially proportional to the capacitance ratio of the sensor and reference capacitors followed by an opposite voltage change due to leakage current through the fuel mixture, whereby the initial voltage change indicates the fuel composition. - View Dependent Claims (2)
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3. A fuel composition sensor for a fuel mixture in a fuel supply line for a combustion engine wherein the fuel mixture comprises two fuels of different dielectric constants in unknown relative concentrations, at least one of the fuels being electrically conductive, the sensor comprising, in combination:
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a sensor capacitor in the fuel line adapted for fuel flow therethrough so that the fuel mixture provided to the engine comprises a dielectric which determines the capacitance thereof but also comprises a capacitor shorting electrical conductance; a reference capacitor of constant capacitance in series with the sensor capacitor to form therewith a voltage divider having an output junction; circuit means for repetitively producing, at a comparatively low frequency, a predetermined fast voltage change across the series combination of the reference and sensor capacitors to produce a corresponding voltage change at the output junction comprising an initial voltage change essentially proportional to the capacitance ratio of the sensor and reference capacitors and defining a peak sensor voltage which indicates the fuel composition, followed by an opposite voltage change due to leakage current through the fuel mixture, whereby the initial voltage change indicates the fuel composition; and a peak detector circuit coupled to the output junction to provide a continuous signal of fuel composition from successive peak sensor voltages. - View Dependent Claims (4, 5, 6, 7, 8)
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Specification