Liquid level and composition sensing systems and methods using EMF wave propagation

• US 20080143345A1
• Filed: 05/08/2007
• Published: 06/19/2008
• Est. Priority Date: 12/18/2006
• Status: Active Grant

• Current Assignee: Schrader Electronics Limited (Sensata Technologies Holding Plc)
• Original Assignee: Schrader Electronics Limited (Sensata Technologies Holding Plc)
• Inventors: Boudaoud, Idir, Page, Adrian M., McCall, Alan Kenneth
• Granted Patent: US 8,482,298 B2
• Time in Patent Office: Days
• US Class Current: 324/652
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/1406 Storage means for substances, e.g. tanks or reservoirs
• CPC Class Codes: F01N 3/206 Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence
• CPC Class Codes: F02D 2200/0611 Fuel type, fuel composition or fuel quality
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01N 27/04 by investigating resistance
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/22 Fuels; Explosives
• CPC Class Codes: G01N 33/2852 Alcohol in fuels
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

An automotive urea solution monitoring device is deployed in conjunction with the urea tank of a selective catalytic reduction vehicle. An RF signal of a constant frequency may be generated across a resonant circuit, which may be comprised of an inductor and a PCB trace capacitor, or the like. Electromagnetic radiation is propagated into the automotive urea solution in the urea tank. The conductivity and dielectric properties of the liquid change the impedance of the discrete/trace capacitor and or the discrete/trace inductor. These changes are proportional to ammonia content, temperature, and/or level of the automotive urea solution in the urea tank and are preferably detected by a microcontroller, or the like, and then transmitted to a selective catalytic reduction vehicle engine management system, or the like.

Claims

1. A method comprising:

generating an RF signal at an operating frequency;

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

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 said liquid is urea.

3. The method of claim 1, wherein said RF signal is substantially sinusoidal and has a constant frequency.

4. The method of claim 1 wherein said resonant circuit is a series-resonant inductor, capacitor, resistor circuit.

5. The method of claim 1 wherein said resonant circuit is a parallel-resonant inductor, capacitor, resistor circuit.

6. The method of claim 1 further comprising placing an inductor of said resonant circuit in close proximity to said tank, causing electromagnetic radiation to propagate into a space defined within said tank, whereby the liquid in said tank acts as an electrical load to said series resonant circuit in a manner proportionate to the constituents of said liquid in said tank.

7. 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.

8. The method of claim 1 wherein the liquid is an automotive urea solution and the variation in said property is a function of liquid composition.

9. The method of claim 1 wherein the liquid is an automotive urea solution and the variation in said property is a function of the ammonia concentration in the automotive urea solution.

10. The method of claim 1 wherein the liquid is a liquid automotive urea solution and the variation in said property is a function of the level of the automotive urea solution in said tank.

11. The method of claim 1, wherein said measuring comprises measuring a change in voltage at the resonant circuit.

12. The method of claim 1, wherein said measuring comprises measuring a change in the resonant frequency of the resonant circuit.

13. The method of claim 1, further comprising calibrating the operating frequency of the RF signal to compensate for physical and/or electrical properties of said tank.

14. The method of claim 13, wherein the operating frequency is calibrated automatically.

15. The method of claim 14, wherein said calibrating the operating frequency comprises sweeping between a range of a frequencies, from a first frequency to a second frequency, to identify said operating signal within said range and measuring a parameter of a resonant circuit from said operating frequency.

16. The method of claim 15 wherein the measured parameter includes the resonant frequency of the resonant circuit.

17. The method of claim 15 wherein the measured parameter includes the amplitude of the resonant frequency of the resonant circuit.

18. The method of claim 1, further comprising transmitting the measured change to an external device.

19. The method of claim 1, further comprising converting the measured change to a value representing a concentration of ammonia in said liquid.

20. A monitoring device comprising:

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

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

a controller, the controller including the RF generator, the controller controlling an operating frequency of the RF generator to be proximate to a resonant frequency of the resonant circuit and measuring a change in an electrical parameter associated with the resonant circuit caused by changes in said liquid in said tank.

21. The device of claim 20, wherein said liquid is an automotive urea solution.

22. The device of claim 21 wherein said changes in said liquid comprises a change in level of said urea in said tank.

23. The device of claim 21 wherein said changes in said liquid comprises a change in concentration of said urea.

24. The device of claim 21 wherein said changes in said liquid comprises a change in ammonia concentration of said urea.

25. The device of claim 20, wherein the controller, antenna driver, and resonant circuit are mounted on a printed circuit board.

26. The device of claim 20, wherein the sensor is installed external to the container or tank.

27. The device of claim 20, wherein the resonant circuit includes a capacitor.

28. The device of claim 27, wherein said capacitor is a printed circuit board trace capacitor.

29. The device of claim 25, wherein said printed circuit board is a flexible printed circuit board.

30. A system 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 a urea tank, the resonant circuit having a resonant frequency; and

a controller operatively connected to the RF generator and to the antenna circuit, the controller being functional to sweep between a range of a frequencies, from a first frequency to a second frequency, to identify a signal at said resonant frequency within said range and measuring a change in an electrical parameter of said signal associated with the resonant circuit caused by changes in a concentration of ammonia in urea in said 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 an ammonia concentration signal and to transmit the ammonia concentration signal to an engine management system of a selective catalytic reduction vehicle.

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 sweep between a range of a frequencies, from a first frequency to a second frequency, to identify a signal at said resonant frequency within said range and measuring a change in an electrical parameter of said signal associated with the resonant circuit caused by changes in concentration of ammonia said urea in said tank.

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

35. The system of claim 30, wherein the controller further comprises a compensation module functional to adjust the ammonia concentration signal for changes in temperature of the liquid in the tank.