System and method for sensing the level and composition of liquid in a fuel tank

• US 20070000321A1
• Filed: 05/10/2006
• Published: 01/04/2007
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: Schrader Electronics Limited (Sensata Technologies Holding Plc)
• Original Assignee: Schrader Electronics Limited (Sensata Technologies Holding Plc)
• Inventors: Boudaoud, Idir, Stewart, William, McCall, Alan
• Granted Patent: US 7,926,341 B2
• Time in Patent Office: Days
• US Class Current: 73/304.R
• CPC Class Codes: G01F 23/22 by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water involving the use of floats G01F23/30
• CPC Class Codes: G01F 23/26 by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
• CPC Class Codes: G01F 23/284 Electromagnetic waves

Abstract

In a liquid sensing system, an RF signal is applied to a series-resonant circuit. The coil of the resonant circuit is placed proximate to a fuel tank, causing electromagnetic radiation to propagate into the fuel space. The fuel acts as an electrical load to the resonant circuit in a manner proportionate to the volume of fuel in the tank and/or to variations in electrical properties of the fuel itself. The loading effect of the fuel can change the resonant frequency and/or the Q of the resonant circuit. The loading effect of the fuel is determined by monitoring a change in one or more electrical parameters associated with the excited resonant circuit, such as a voltage across the resistor in the resonant circuit. Changes in this voltage are analyzed by a controller, the result of which is used to output a value indicative of level and/or composition of the fuel.

Claims

1. A method of sensing a property of a liquid in a container comprising

(a) generating an RF signal at an operating frequency;

(b) coupling the RF signal to a resonant circuit, the resonant circuit having a resonant frequency and including an inductor positioned proximate to the liquid in the container; and

(c) measuring a change in an electrical parameter associated with the resonant circuit caused by a variation in at least one property of the liquid proximate to the inductor.

2. The method of claim 1 wherein the at least one property of the liquid in the container is volume and the measured change in the electrical parameter is a function of a variation in the volume of the liquid in the container.

3. The method of claim 2, wherein the volume of the liquid in the entire container is measured.

4. The method of claim 2, wherein the volume of the liquid in a portion of the container is measured.

5. The method of claim 2, further comprising:

after step (c), converting the measured change to a value representing the volume of the liquid in the container

6. The method of claim 1 wherein the at least one property of the liquid is an electrical property and the measured change in the electrical parameter is a function of a variation in the electrical property of the liquid in the container.

7. The method of claim 6 wherein the liquid is a fuel, the container is a fuel tank, and the variation in electrical property is a function of fuel composition.

8. The method of claim 1, wherein step (c) comprises measuring a change in voltage at the resonant circuit.

9. The method of claim 1, wherein step (c) comprises measuring a change in the resonant frequency of the resonant circuit.

10. The method of claim 1, further comprising:

prior to step (a), calibrating the operating frequency of the RF signal to compensate for physical and/or electrical properties of the container.

11. The method of claim 10, wherein the operating frequency is calibrated automatically.

12. The method of claim 10, wherein the step of calibrating the operating frequency comprises:

adjusting the operating frequency of the RF signal so that a liquid volume sensing window is defined on a substantially linear part of a frequency response curve proximate the resonant frequency of the resonant circuit.

13. The method of claim 10, wherein the step of calibrating the operating frequency comprises:

sweeping the operating frequency of the RF signal in a range between a first frequency and a second frequency; and

measuring a parameter of the resonant circuit as the frequency of the RF signal is swept.

14. The method of claim 13 wherein the first frequency is approximately 7.4 MHz and the second frequency is approximately 8.3 MHz.

15. The method of claim 1, further comprising:

prior to step (b), amplifying the RF signal.

16. The method of claim 1, further comprising:

after step (c), transmitting the measured change to an external device.

17. A method for measuring the volume of fuel in a fuel tank comprising:

(a) generating an RF signal at an operating frequency;

(b) coupling the RF signal to a resonant circuit having an inductor, where the inductor is proximate the fuel in the tank;

(c) measuring a change in value of a variable electrical parameter of the resonant circuit; and

(d) converting the measured change to a fuel volume.

18. The method of claim 17, further comprising:

prior to step (a), calibrating the operating frequency of the RF signal to account for variations between fuel tanks.

19. The method of claim 17, wherein step (d) comprises:

compensating the measured change for ambient temperature; and

calculating the volume of fuel in the tank using the compensated value.

20. The method of claim 17, further comprising:

after step (d), transmitting the converted value.

21. The method of claim 20, wherein the converted value is transmitted via a physical interface.

22. The method of claim 20, wherein the converted value is transmitted via a wireless interface.

23. The method of claim 17 further comprising:

prior to step (d), transmitting the measure change in value.

24. An apparatus for measuring the volume of liquid in a container comprising:

a controller, the controller including an RF generator and an analog-to-digital converter (ADC);

an antenna driver having output terminals, and input terminals, coupled to the RF generator; and

a resonant circuit coupled to the antenna driver and having an inductor positioned proximate the liquid in the container.

25. The apparatus of claim 24, wherein the controller, antenna driver, and resonant circuit are mounted on a printed circuit board.

26. The apparatus of claim 24, wherein the apparatus is installed external to the container.

27. The apparatus of claim 24 wherein at least the inductor of the resonant circuit is installed internal to the container.

28. The apparatus of claim 24, further comprising a ground plane positioned proximate the inductor such that the inductor is positioned between the ground plane and the container and RF energy from the inductor is directed towards a particular part of the container.

29. The apparatus of claim 24 wherein the inductor of the resonant circuit is positioned inside the container and further comprising a ground plane positioned between the inductor and the container.

30. A system for measuring a level of fuel in a non-metal fuel tank mounted in a motor vehicle, the system comprising:

a vehicle data bus;

an RF generator functional to generate an RF signal at an operating frequency;

an antenna circuit electrically coupled to the RF generator, the antenna circuit comprising a resonant circuit and a radiating component mounted proximate to the fuel tank, the resonant circuit having a frequency response curve centered around a resonant frequency;

a controller operatively connected to the RF generator and to the antenna circuit, the controller being functional

to cause the operating frequency of the RF generator to be proximate to the resonant frequency of the resonant circuit, and

to measure a change in an electrical parameter associated with the resonant circuit caused by changes in the level of fuel in the fuel tank.

31. The system of claim 30 wherein the controller is further functional to transmit the measured change in the electrical parameter.

32. The system of claim 30 wherein the controller is further functional to convert the measured change in the electrical parameter to a fuel level signal and to transmit the fuel level signal to said vehicle data bus.

33. The system of claim 30, wherein:

the resonant circuit is a series resonant circuit; and

the controller further comprises a calibration module operative to cause the operating frequency of the RF generator to be on a substantially linear portion of the frequency response curve above the resonant frequency.

34. The system of claim 30, wherein the controller further comprises a compensation module functional to adjust the fuel level signal for changes in ambient temperature.

35. The system of claim 30, wherein the controller further comprises a compensation module functional to adjust the fuel level signal for changes in electrical properties of the fuel in the tank.

36. The system of claim 30 further comprising a ground plane mounted in the vehicle proximate the radiating component such that the radiating component is positioned between the ground plane and the fuel tank, the ground plane and radiating component electrically cooperating to direct RF energy from the radiating component to a selected region of the fuel tank.

37. The system of claim 30 wherein the radiating component is positioned inside the fuel tank and further comprising a ground plane positioned between the inductor and the tank.

38. A method of sensing a property of fuel in a fuel tank comprising:

(a) generating an RF signal at an operating frequency;

(b) coupling the RF signal to a resonant circuit, the resonant circuit having a resonant frequency and including an inductor positioned proximate to the fuel in the tank; and

(c) measuring a change in an electrical parameter associated with the resonant circuit;

wherein the change in the electrical parameter is a caused by variations in a property of the fuel in the container.

39. The method of claim 38 wherein the property of the fuel in the container comprises fuel composition and wherein the method further comprises comparing the measured change in electrical parameter with stored profiles associated with known fuel compositions.

40. A system for use in measuring a property of fuel in a vehicle fuel tank comprising:

an RF generator functional to generate an RF signal at an operating frequency;

an antenna circuit electrically coupled to the RF generator, the antenna circuit comprising a resonant circuit and a radiating component mounted proximate to the fuel in the tank, the resonant circuit having a frequency response curve centered around a resonant frequency;

a controller operatively connected to the RF generator and to the antenna circuit, the controller being functional

to cause the operating frequency of the RF generator to be proximate to the resonant frequency of the resonant circuit,

to measure a change in an electrical parameter associated with the resonant circuit caused by variations in electrical properties associated with different compositions of the fuel in the tank, and

to measure a change in an electrical parameter associated with the resonant circuit caused by variations in the property of the fuel in the fuel tank.

41. The system of claim 40, wherein:

the resonant circuit is a series resonant circuit; and

the controller further comprises a calibration module operative to cause the operating frequency of the RF generator to be on a substantially linear portion of the frequency response curve above the resonant frequency.

42. The system of claim 40 wherein the property of the fuel includes fuel volume.

43. The system of claim 40 wherein the property of the fuel includes fuel composition.