Self Calibrating Capacitive Fuel Sensor
A method and apparatus are provided for determining a level of fuel in a tank, comprising determining a dielectric constant of fuel in a tank; measuring a capacitance of an unknown depth of the fuel in the tank; and calculating the depth using the dielectric constant and the capacitance. Embodiments of the apparatus utilize a capacitor plate submerged in the fuel to determine the dielectric constant of the fuel, and then use a plate of a separate capacitor to determine the fuel level, once the dielectric constant is known.
1 . A self-calibrating liquid fuel level sensor, comprising:
a calibrator that determines a dielectric constant of a liquid fuel;
a fuel depth capacitance sensor that determines a capacitance of an unknown depth of the fuel; and
a processor that calculates a determined depth based on the unknown depth using the dielectric constant and the capacitance.
2 . The sensor of claim 1 , further comprising:
a first conductive member that acts as a charge plate of a first capacitor;
a second conductive member that is electrically isolated from the first conductor member that acts as a charge plate of a second capacitor ; and
a third conductive member that acts as an opposite charge plate of the first capacitor and the second capacitor;
wherein the calibrator comprises the first conductive member, the third conductive member, and elements for determining capacitance including a processor comprising algorithms.
3 . The sensor of claim 1 , wherein:
the third conductive member is a hollow cylinder; and
the first and second conductive members are each hollow cylinders that reside concentrically within the third conductive member.
4 . The sensor of claim 1 , wherein the elements for determining capacitance comprise:
a resistor that is connected to the first conducting member through which the first capacitor and the second capacitor may be at least one of charged and discharged; and
a controller that measures at least one of charge and discharge times of the first and second capacitors to determine capacitance of the first and second capacitors using a standard exponential charge and discharge formula for resistor capacitor networks.
5 . The sensor of claim 4 , further comprising:
a charge-discharge switch that alternately applies a ground or a voltage signal to one end of the resistor, the other end of the resistor being connected to the first capacitor.
6 . The sensor of claim 5 , wherein the controller operates the switch based on a threshold value.
7 . The sensor of claim 4 , further comprising:
a parallel capacitor switch that alternately connects or disconnects the second capacitor in parallel with the first capacitor between ground and an other end of the resistor.
8 . A method of determining a level of fuel in a tank, comprising:
determining a dielectric constant of fuel in a tank;
measuring a capacitance of an unknown depth of the fuel in the tank; and
calculating the depth using the dielectric constant and the capacitance.
9 . The method of claim 8 , wherein the determining of the dielectric constant comprises:
providing a first conducting member that acts as a charge plate of a first capacitor;
providing a second conductive member that is electrically isolated from the first conductor member that acts as a charge plate of a second capacitor;
providing a third conductive member that acts as an opposite charge plate of the first capacitor and the second capacitor;
completely submerging the first conducting member in the fuel;
measuring a capacitance of the first capacitor; and
calculating the dielectric constant based on the measured capacitance of the first capacitor.
10 . The method of claim 9 , wherein measuring the capacitance comprises:
connecting a resistor to the first conducting member through which the first capacitor and the second capacitor may be at least one of charged and discharged; and
measuring, using a controller, at least one of a charge and a discharge time of the first and second capacitors to determine capacitance of the first and second capacitors using a standard exponential charge and discharge formula for resistor capacitor networks.
11 . The method of claim 10 , further comprising:
operating a charge-discharge switch to alternately apply a ground or a voltage signal to one end of the resistor, the other end of the resistor being connected to the first capacitor.
12 . The method of claim 11 , further comprising:
detecting a threshold value by the controller; and
triggering the operating of the charge-discharge switch based on exceeding the threshold value.
13 . The method of claim 10 , further comprising:
operating a parallel capacitor switch that alternately connects or disconnects the second capacitor in parallel with the first capacitor between ground and an other end of the resistor.
14 . The method of claim 9 , wherein:
the third conductive member is a hollow cylinder; and
the first and second conductive members are each hollow cylinders that reside concentrically within the third conductive member.