Importance

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Abstract

A fuel composition sensor for a fuel line carrying a mixture of two fuels provides a fuel composition signal VOUT to an engine control computer having a computer analog reference voltage ECM referenced to a computer ground EGD. The sensor has a sensor analog reference voltage VREF referenced to a sensor ground GND, which may differ from the computer ground EGD. An input isolation amplifier derives the sensor analog reference voltage VREF relative to GND ratiometrically from the computer analog reference voltage ECM referenced to EGD; and an output isolation amplifier derives the fuel composition signal VOUT referenced to EGD ratiometrically from the difference between a fuel composition responsive sensor signal VSIG and its minimum possible value, corresponding to a sensed fuel composition of only one of the fuels, relative to GND. The sensor may comprise a capacitive voltage divider and provide sensor voltage VSIG also having a maximum value corresponding to a sensed fuel composition of only the other fuel. If the range of possible values of VSIG is compressed, the isolation amplifier may provide a gain greater than one to better match the available input range of the computer. The minimum value of the fuel composition signal may be set detectably greater than EGD so that a value of EGD signals a sensor fault.

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First Claim