Fuel gaging system
AssigneeThe Boeing Company
InventorRobert G. Brasfield
Life of this patent
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Abstract
A fuel gaging system of the type wherein the capacitance of a probe (20) within the fuel tank is used as an indication of fuel quantity via an assumed density/dielectric constant relationship (10) of the fuel. System accuracy is improved by directly measuring fuel density and dielectric constant. These values are compared with the assumed values in a processor (68) which generates an appropriate gaging correction signal in response to a discrepancy.
Claims14
In a fuel gaging system wherein fuel quantity is determined by measuring the capacitance of a capacitive probe in the fuel tank and relating such capacitance to fuel mass by a predetermined fuel density/fuel dielectric constant relationship, the improvement comprising:
- means for producing a signal K representative of the actual dielectric constant of the fuel;
- means for producing a signal D.sub.A representative of the actual density of the fuel;
- and
- processor means for processing said K and D.sub.A signals and determining whether said predetermined relationship is valid for the particular fuel in the tank and, if said predetermined relationship is invalid, applying a predetermined correction signal to said gaging system such that said system indicates actual fuel mass.
Apparatus for producing an indication of the quantity of fuel in a tank comprising:
- a capacitive fuel probe in the tank, the probe exhibiting a capacitance which is a function of fluid level in the tank and of the dielectric constant of the fuel;
- a compensator capacitor connected in series with said capacitive fuel probe and positioned in the tank such that it is wetted by fuel for all fuel levels, the compensator capacitor exhibiting a capacitance which is a function of the dielectric constant of the fuel;
- means for applying a predetermined level periodic A.C. signal to the free end of the capacitive fuel probe;
- variable signal means for applying a 180.degree. phase shifted variable level of said periodic A.C. signal to the free end of the compensator capacitor;
- means for controlling the signal level produced by said variable signal means such that a signal null is produced at the junction of the capacitive fuel probe and the compensator capacitor, the level of signal produced by the variable signal means being indicative of fuel quantity in the tank;
- means for determining the actual dielectric constant K of the fuel, said means including means for producing a sense signal in quadrature with said periodic A.C. signal and applying said sense signal to said compensator capacitor and further means for processing said sense signal and determining said dielectric constant K in response thereto;
- means for determining the actual density D.sub.A of the fuel;
- and
- correction signal means for producing a correction signal responsive to the actual dielectric constant and density of the fuel and using said signal as a correction factor to the fuel quantity indication.
In a fuel gaging system wherein fuel quantity is determined by measuring the capacitance of a capacitive probe in the fuel tank and relating such capacitance to fuel mass by a predetermined fuel density/fuel dielectric constant relationship, a method for correcting fuel gaging errors due to a deviation of the actual fuel in the tank from said predetermined relationship, the method comprising the steps of:
- (a) producing a signal K representative of the actual dielectric constant of the fuel;
- (b) producing a signal D.sub.A representative of the actual density of the fuel;
- and
- (c) processing said K and D.sub.A signals and determining whether said predetermined relationship is valid for the particular fuel in the tank and, if said predetermined relationship is invalid, applying a predetermined correction signal to said gaging system such that said system indicates actual fuel quantity.
Dependencies are inferred from the claim text.