Electrical field sensors for detecting fluid presence or level

• US 7,432,725 B2
• Filed: 03/15/2006
• Issued: 10/07/2008
• Est. Priority Date: 03/15/2006
• Status: Expired due to Fees

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Sieh, Philip J., Stewart, Bradley C., Steffen, Michael A.
• Primary Examiner(s): Nguyen; Vincent Q.
• Assistant Examiner(s): Natalini; Jeff
• Application Number:
  US11/376,810
• Publication Number:
  US 20070216424A1
• Time in Patent Office: 937 Days
• Field of Search: 324/551
• US Class Current: 324/662
• CPC Class Codes: G01F 23/268 mounting arrangements of probes
• CPC Class Codes: G01R 29/12 Measuring electrostatic fields or voltage-potential

Abstract

The present disclosure provides several systems. In general, it provides E-field sensor systems that utilize at least one electrode 100 adapted for creating an E-field in an area 210 within a detection volume where fluid presence 400 or presence of a solid body 300 is to be detected. The electrical field sensor is configured to generate a detected signal responsive to a change in capacitance of the electric field, and is communicatively coupled to the electrode 100. In addition, a processor 275 is configured to determine a quantitative measure of a fluid or solid body within the detection volume in accordance with a capacitive relationship with the detection volume. Described are examples of the system for fluid presence detection, fluid level measurement and measurement of proximity to a solid object.

Claims

1. An electric field sensor system comprising:

a first electrode adapted for creating an electric field in an area within a detection volume where fluid presence or level is to be detected;

a second electrode communicatively coupled to the first electrode;

a reference electrode;

an electrical field sensor communicatively coupled to the first electrode and to the reference electrode, the electrical field sensor configured to generate a detected signal responsive to a change in the electric field; and

a processor coupled to the field sensor, the processor configured to determine;

(i) the dielectric constant of a fluid within the detection volume utilizing the reference electrode, and (ii) a quantitative measure of the fluid within the detection volume from the dielectric constant and the detected signal in accordance with a capacitive relationship between the first electrode, the detection volume and fluid properties.

2. The system of claim 1, wherein the first electrode comprises a first series of discrete electrodes, the discrete electrodes arrayed to each create an E-field in an area in a vicinity of the electrode.

3. The system of claim 2, wherein the capacitive relationship comprises:

C=[kε

₀A/d]

where C is capacitance, k is a dielectric constant of fluid to be detected, d is a characteristic dimension, ε

₀ is the permittivity of free space, and A is an electrode surface area.

4. The system of claim 1, wherein the first electrode comprises a first continuous strip electrode or a series of ring electrodes or a series of strip electrodes.

5. The system of claim 4, wherein the first electrode is a substantially uniformly rectangular strip, and the ground plate or second electrode comprise dimensions substantially identical to the first electrode.

6. The system of claim 5, wherein the capacitive relationship comprises:

C=[kε

₀A/d]

where C is detected capacitance, k is a dielectric constant of a fluid to be detected, d is a characteristic dimension, ε

₀ is the permittivity of free space, and A is an electrode surface area.

7. The system of claim 1, wherein the capacitive relationship comprises:

C=[kε

₀A/d]

where C is detected capacitance, k is a dielectric constant of a fluid to be detected, d is a distance between the electrodes, ε

₀ is the permittivity of free space, and A is an electrode surface area.

8. The system of claim 7, wherein inputs to the processor comprise a relationship between fluid quantitative measure, capacitance and a ratio of an area A₁ of the first electrode to an area A₂ of the second electrode.

9. A sensor system comprising:

a first electrode and a second electrode adapted to create a first electric field within a detection volume;

a pair of reference electrodes adapted to create a second electric field proximate the detection volume;

an electrical field sensor communicatively coupled to the first and second electrodes and to the pair of reference electrodes, the electrical field sensor configured to generate a first signal responsive to a change in the first electric field and a second signal indicative of a change in the second electric field; and

a processor coupled to the electrical field sensor, the processor configured to determine;

(i) the dielectric constant of a fluid within the detection volume utilizing the second signal, and (ii) a quantitative measure of the fluid within the detection volume from the first signal in accordance with the dielectric constant and a predetermined relationship between the fluid quantitative measure and a ratio of an area A₁ of the first electrode to an area A₂ of the second electrode.

10. The system of claim 9, wherein the pair of reference electrodes is disposed such that the horizontal center of the pair of reference electrodes is positioned beneath the horizontal center of the first electrode.

11. The system of claim 9, wherein the pair of reference electrodes is located to sense fluid continuously while the system is in use.

12. The system of claim 9, wherein the first electrode comprises a triangular strip and the second electrode comprises a complementary triangular strip, such that summing equal length complementary segments provides a constant area.

13. An electric filed sensor system for detecting proximity to the vertical drum of a laundry machine, the system comprising:

a grid of electrodes in a plane parallel to a base of the drum adapted to create an electric field within a detection volume comprising the drum, the electrodes aligned spatially from a portion of an outer surface of the drum in the electric field;

an electrical field sensor communicatively coupled to the electrodes, the electrical field sensor configured to generate a signal responsive to a change in the electric field; and

a processor coupled to the electrical field sensor, the processor configured to determine a displacement measure of the drum within the detection volume from the signal in accordance with a predetermined capacitive relationship between the electrodes, the detection volume, and the drum;

wherein the capacitive relationship comprises;

C=[kε

₀A/d]

where C is detected capacitance, k is a dielectric constant of an object to be detected, ε

₀ is the permittivity of free space, and A is an electrode surface area, and d is a characteristic displacement dimension.

14. An electric field sensor system for detecting the proximity of a horizontal drum of a front loading laundry machine, the system comprising:

an array of electrodes aligned in a plane parallel to an axis of rotation of the drum and adapted to create an electric field within a detection volume comprising the drum, the electrodes aligned spatially from a portion of an outer surface of the drum in the electric field;

an electrical field sensor communicatively coupled to the electrodes, the electrical field sensor configured to generate a signal responsive to a change in the electric field; and

a processor coupled to the electrical field sensor, the processor configured to determine a displacement measure of the drum within the detection volume from the signal in accordance with a predetermined capacitive relationship between the electrodes, the detection volume, and the drum;

wherein the capacitive relationship comprises;

C=[kε

₀A/d]

where C is detected capacitance, k is a dielectric constant of an object to be detected, ε

₀ is the permittivity of free space, and A is an electrode surface area, and d is a characteristic displacement dimension.